Acme thread

Machinery's Handbook 27th EditionACME SCREW THREADS1825ACME SCREW THREADSAmerican National Standard Acme Screw ThreadsThis American National Standard ASME/ANSI B1.5-1997 is a revision of AmericanStandard ANSI B1.5-1988 and provides for two general applications of Acme threads,namely, General Purpose and limits and tolerances in this standard relate to single-start Acme threads, and may beused, if considered suitable, for multi-start Acme threads, which provide fast relative tra-versing motion when this is necessary. For information on additional allowances for multi-start Acme threads, see later section on l Purpose Acme Threads.—Three classes of General Purpose threads, 2G, 3G,and 4G, are provided in the standard, each having clearance on all diameters for free move-ment, and may be used in assemblies with the internal thread rigidly fixed and movementof the external thread in a direction perpendicular to its axis limited by its bearing or bear-ings. It is suggested that external and internal threads of the same class be used together forgeneral purpose assemblies, Class 2G being the preferred choice. If less backlash or endplay is desired, Classes 3G and 4G are provided. Class 5G is not recommended for Form: The accompanying Fig. 1 shows the thread form of these General Purposethreads, and the formulas accompanying the figure determine their basic 1 gives the basic dimensions for the most generally used of Thread: The angle between the sides of the thread, measured in an axial plane, is29 degrees. The line bisecting this 29-degree angle shall be perpendicular to the axis of thescrew Series: A series of diameters and associated pitches is recommended in the Stan-dard as preferred. These diameters and pitches have been chosen to meet present needswith the fewest number of items in order to reduce to a minimum the inventory of bothtools and gages. This series of diameters and associated pitches is given in Table rs and Fillets: General Purpose external threads may have the crest corner cham-fered to an angle of 45 degrees with the axis to a maximum width of P/15, where P is thepitch. This corresponds to a maximum depth of chamfer fiat of Diameters: The max major diameter of the external thread is basic and is the nom-inal major diameter for all classes. The min pitch diameter of the internal thread is basicand is equal to the basic major diameter minus the basic height of the thread, h. The basicminor diameter is the min minor diameter of the internal thread. It is equal to the basicmajor diameter minus twice the basic thread height, of Engagement: The tolerances specified in this standard are applicable tolengths of engagement not exceeding twice the nominal major and Minor Diameter Allowances: A minimum diametral clearance is provided atthe minor diameter of all external threads by establishing the maximum minor diameter0.020 inch below the basic minor diameter of the nut for pitches of 10 threads per inch andcoarser, and 0.10 inch for finer pitches. A minimum diametral clearance at the major diam-eter is obtained by establishing the minimum major diameter of the internal thread 0.020inch above the basic major diameter of the screw for pitches of 10 threads per inch andcoarser, and 0.010 inch for finer and Minor Diameter Tolerances: The tolerance on the external thread majordiameter is 0.05P, where P is the pitch, with a minimum of 0.005 inch. The tolerance on theinternal thread major diameter is 0.020 inch for 10 threads per inch and coarser and 0.010for finer pitches. The tolerance on the external thread minor diameter is 1.5 × pitch diame-ter tolerance. The tolerance on the internal thread minor diameter is 0.05P with a minimumof 0.005 ght 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th Edition1826ACME SCREW THREADSANSI General Purpose Acme Thread Form ASME/ANSI B1.5-1997, and Stub Acme Screw Thread Form ASME/ANSI B1.8-1988 (R2001)Fig. 1. General Purpose and Stub Acme Thread FormsFormulas for Basic Dimensions of General Purpose and Stub Acme Screw ThreadsGeneral PurposePitch = P = 1 ÷ No. threads per inch, nBasic thread height h = 0.5PBasic thread thickness t = 0.5PBasic flat at crest Fcn = 0.3707P (internal

thread)Basic flat at crest Fcs = 0.3707P − 0.259 ×

(pitch dia. allowance on ext. thd.)Frn = 0.3707P − 0.259 × (major dia. allowanceon internal thread)Frs = 0.3707P − 0.259 × (minor dia. allowanceon ext. thread − pitch dia.

allowance on ext. thread)Stub Acme ThreadsPitch = P = 1 ÷ No. threads per inch, nBasic thread height h = 0.3PBasic thread thickness t = 0.5PBasic flat at crest Fcn = 0.4224P (internal

thread)Basic flat at crest Fcs = 0.4224P − 0.259 ×(pitch dia. allowance on ext. thread)Frn = 0.4224P − 0.259 × (major dia. allowanceon internal thread)Frs = 0.4224P − 0.259 × (minor dia. allowanceon ext. thread − pitch dia. allowanceon ext. thread)Pitch Diameter Allowances and Tolerances: Allowances on the pitch diameter of Gen-eral Purpose Acme threads are given in Table 4. Pitch diameter tolerances are given inTable 5. The ratios of the pitch diameter tolerances of Classes 2G, 3G, and 4G, GeneralPurpose threads are 3.0, 1.4, and 1, increase of 10 per cent in the allowance is recommended for each inch, or fractionthereof, that the length of engagement exceeds two ation of Tolerances: The tolerances specified are designed to ensure interchange-ability and maintain a high grade of product. The tolerances on diameters of the internalthread are plus, being applied from minimum sizes to above the minimum sizes. The toler-ances on diameters of the external thread are minus, being applied from the maximum sizesto below the maximum sizes. The pitch diameter (or thread thickness) tolerances for anexternal or internal thread of a given class are the same. The thread thickness tolerance is0.259 times the pitch diameter ght 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionACME SCREW THREADS1827Limiting Dimensions: Limiting dimensions of General Purpose Acme screw threads inthe recommended series are given in Table 2b. These limits are based on the formulas inTable combinations of pitch and diameter other than those in the recommended series, theformulas in Table 2a and the data in Tables 4 and 5 make it possible to readily determinethe limiting dimensions required.A diagram showing the disposition of allowances, tolerances, and crest clearances forGeneral Purpose Acme threads appears on Area of General Purpose Acme Threads: For computing the tensile strength of thethread section, the minimum stress area based on the mean of the minimum pitch diameterd2 min. and the minimum minor diameter d1 max. of the external thread is used:d2 min.+d1 max.⎞2Stress Area=3.1416⎛-------------------------------------------⎝⎠4where d2 min. and d1 max. may be computed by Formulas 4 and 6, Table 2a or taken fromTable Area of General Purpose Acme Threads: For computing the shear area per inchlength of engagement of the external thread, the maximum minor diameter of the internalthread D1 max., and the minimum pitch diameter of the external thread D2 min., Table 2bor Formulas 12 and 4, Table 2a, are used:Shear Area=3.1416D1 max. [0.5+ntan141⁄2°(D2 min.–D1 max.)]Acme Thread Abbreviations.—The following abbreviations are recommended for useon drawings and in specifications, and on tools and gages:ACME=Acme threadsG=General PurposeC=CentralizingP=pitchL=leadLH=left handDesignation of General Purpose Acme Threads.—The examples listed below aregiven here to show how General Purpose Acme threads are designated on drawings andtools:1.750-4 ACME-2G indicates a General Purpose Class 2G Acme thread of 1.750-inchmajor diameter, 4 threads per inch, single thread, right hand. The same thread, but lefthand, is designated 1.750-4 ACME-2G-LH.2.875-0.4P-0.8L-ACME-3G indicates a General Purpose Class 3G Acme thread of2.875-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double thread, right le Start Acme Threads.—The tabulated diameter-pitch data with allowances andtolerances relate to single-start threads. These data, as tabulated, may be and often are usedfor two-start Class 2G threads but this usage generally requires reduction of the full work-ing tolerances to provide a greater allowance or clearance zone between the mating threadsto assure satisfactory the class of thread requires smaller working tolerances than the 2G class or whenthreads with 3, 4, or more starts are required, some additional allowances or increased tol-erances or both may be needed to ensure adequate working tolerances and satisfactoryassembly of mating is suggested that the allowances shown in Table 4 be used for all external threads andthat allowances be applied to internal threads in the following ratios: for two-start threads,50 per cent of the allowances shown in the Class 2G, 3G and 4G columns of Table 4; forCopyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th Edition1828ACME SCREW THREADSTable 1. American National Standard General Purpose Acme Screw Thread Form

— Basic Dimensions ASME/ANSI hn4321⁄2211⁄211⁄3Height ofThread(Basic),h = P/20.031250.035710.041670.050000.062500.083330.100000.125000.166670.200000.250000.333330.375000.50000TotalHeight ofThread,hs = P/2 +

1⁄2allowancea0.03620.04070.04670.06000.07250.09330.11000.13500.17670.21000.26000.34330.38500.5100Width of FlatThreadThickness(Basic),t = P/20.031250.035710.041670.050000.062500.083330.100000.125000.166670.200000.250000.333330.375000.50000Crest of

Internal Thread(Basic),Fcn = 0.3707P0.02320.02650.03090.03710.04630.06180.07410.09270.12360.14830.18530.24710.27800.3707Root of InternalThread, Frn0.3707P −0.259 ×allowancea0.02060.02390.02830.03190.04110.05660.06890.08750.11840.14310.18020.24190.27280.3655Pitch,P = 1/n0.062500.071430.083330.0100000.125000.166670.200000.250000.333330.400000.500000.666670.7500011.00000All dimensions are in inches.a

Allowance is 0.020 inch for 10 threads per inch and coarser, and 0.010 inch for finer threads.

Table 2a. American National Standard General Purpose Acme Single-Start Screw

Threads — Formulas for Determining Diameters ASME/ANSI B1.5-1997D = Basic Major Diameter and Nominal Size, in Inches.P = Pitch = 1 ÷ Number of Threads per Inch.E = Basic Pitch Diameter = D − 0.5PK = Basic Minor Diameter = D − PNo.123456Major Dia., Max. = DMajor Dia., Min. = D minus 0.05Pa but not less than Dia., Max. = E minus allowance from Table Dia., Min. = Pitch Dia., Max. (Formula 3) minus tolerance from Table Dia., Max. = K minus 0.020 for 10 threads per inch and coarser and 0.010 for Dia., Min. = Minor Dia., Max. (Formula 5) minus 1.5 × pitch diameter tolerance

from Table al Threads (Nuts)Major Dia., Min. = D plus 0.020 for 10 threads per inch and coarser and 0.010 for finer

Dia., Max. = Major Dia., Min. (Formula 7) plus 0.020 for 10 threads per inch andcoarser and 0.010 for finer Dia., Min. = EPitch Dia., Max. = Pitch Dia., Min. (Formula 9) plus tolerance from Table Dia., Min. = KMinor Dia., Max. = Minor Dia., Min. (Formula 11) plus 0.05Pa but not less than al Threads (Screws)789101112a

If P is between two recommended pitches listed in Table 3, use the coarser of the two pitches in thisformula instead of the actual value of P.

Copyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionTable 2b. Limiting Dimensions of ANSI General Purpose Acme Single-Start Screw Threads ASME/ANSI B1.5-1988Nominal Diameter, D1⁄45⁄163⁄87⁄161⁄25⁄83⁄47⁄8111⁄811⁄413⁄8Threads per Incha665554Limiting DiametersExternal ThreadsClasses 2G, 3G, and 4GMajor Diameter{Max (D)0.25000.31250.37500.43750.50000.62500.75000.87501.00001.12501.25001.3750Min0.24500.30750.37000.43250.49500.61880.74170.86670.99001.11501.24001.3625Classes 2G, 3G, and 4GMinor DiameterMax0.17750.23110.28170.34420.38000.48000.56330.68830.78000.90501.03001.1050Class 2G, Minor DiameterMin0.16180.21400.26320.32530.35940.45700.53720.66150.75090.87530.99981.0720Class 3G, Minor DiameterMin0.17020.22310.27300.33540.37040.46930.55110.67580.76640.89121.01591.0896Class 4G, Minor DiameterMin0.17220.22540.27550.33790.37310.47230.55460.67940.77030.89511.01991.0940Class 2G, Pitch Diameter{Max0.21480.27280.32840.39090.44430.55620.65980.78420.89201.01651.14111.2406Min0.20430.26140.31610.37830.43060.54080.64240.76630.87260.99671.12101.2188Class 3G, Pitch Diameter{Max0.21580.27380.32960.39210.44580.55780.66150.78610.89401.01861.14331.2430Min0.21090.26850.32380.38620.43940.55060.65340.77780.88491.00941.13391.2327Class 4G, Pitch Diameter{Max0.21680.27480.33090.39340.44720.55930.66320.78800.89601.02081.14551.2453Min0.21330.27100.32680.38920.44260.55420.65740.78200.88951.01421.13881.2380Internal ThreadsClasses 2G, 3G, and 4G{Min0.26000.32250.38500.44750.52000.64500.77000.89501.02001.14501.27001.3950Major DiameterMax0.27000.33250.39500.45750.54000.66500.79000.91501.04001.16501.29001.4150Classes 2G, 3G, and 4GMin0.18750.24110.29170.35420.40000.50000.58330.70830.80000.92501.05001.1250Minor Diameter{Max0.19250.24610.29670.35920.40500.50620.59160.71660.81000.93501.06001.1375Class 2G, Pitch Diameter{Min0.21880.27680.33330.39580.45000.56250.66670.79170.90001.02501.15001.2500Max0.22930.28820.34560.40840.46370.57790.68410.80960.91941.04481.17011.2720Class 3G, Pitch Diameter{Min0.21880.27680.33330.39580.45000.56250.66670.79170.90001.02501.15001.2500Max0.22370.28210.33910.40170.45640.56970.67480.80000.90911.03421.15941.2603Class 4G, Pitch Diameter{Min0.21880.27680.33330.39580.45000.56250.66670.79170.90001.02501.15001.2500Max0.22230.28060.33740.40000.45460.56760.67250.79770.90651.03161.15671.2573Copyright 2004, Industrial Press, Inc., New York, NYACME SCREW THREADS1829

Machinery's Handbook 27th EditionTable 2b. (Continued) Limiting Dimensions of ANSI General Purpose Acme Single-Start Screw Threads ASME/ANSI B1.5-1988Nominal Diameter, D11⁄13⁄221⁄21⁄23⁄331⁄441⁄5Threads per Incha44433322222Limiting DiametersExternal ThreadsClasses 2G, 3G, and 4GMajor Diameter{Max (D)1.50001.75002.00002.25002.50002.75003.00003.50004.00004.50005.0000Min1.48751.73751.98752.23332.48332.73332.97503.47503.97504.47504.9750Classes 2G, 3G, and 4GMinor DiameterMax1.23001.48001.73001.89672.14672.39672.48002.98003.48003.98004.4800Class 2G, Minor DiameterMin1.19651.44561.69481.85722.10652.35582.43262.93143.43023.92914.4281Class 3G, Minor DiameterMin1.21441.46401.71361.87832.12792.37762.45792.95743.45683.95634.4558Class 4G, Minor DiameterMin1.21891.46861.71831.88352.13332.38312.46422.96383.46343.96314.4627Class 2G, Pitch Diameter{Max1.36521.61451.86372.07132.32072.57002.73603.23503.73404.23304.7319Min1.34291.59161.84022.04502.29392.54272.70443.20263.70084.19914.6973Class 3G, Pitch Diameter{Max1.36771.61711.86652.07432.32382.57342.73953.23883.73804.23734.7364Min1.35731.60641.85552.06202.31132.56072.72483.22373.72254.22154.7202Class 4G, Pitch Diameter{Max1.37011.61981.86932.07732.32702.57672.74303.24253.74204.24154.7409Min1.36271.61221.86152.06852.31812.56762.73253.23173.73094.23024.7294Internal ThreadsClasses 2G, 3G, and 4GMin1.52001.77002.02002.27002.52002.77003.02003.52004.02004.52005.0200Major Diameter{Max1.54001.79002.04002.29002.54002.79003.04003.54004.04004.54005.0400Classes 2G, 3G, and 4GMin1.25001.50001.75001.91672.16672.41672.50003.00003.50004.00004.5000Minor Diameter{Max1.26251.51251.76251.93342.18342.43342.52503.02503.52504.02504.5250Min1.37501.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Class 2G, Pitch Diameter{Max1.39731.64791.89852.10962.36012.61062.78163.28243.78324.28394.7846Min1.37501.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Class 3G, Pitch Diameter{Max1.38541.63571.88602.09562.34582.59602.76473.26513.76554.26584.7662Min1.37501.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Class 4G, Pitch Diameter{Max1.38241.63261.88282.09212.34222.59242.76053.26083.76114.26134.7615a

All other dimensions are given in inches. The selection of threads per inch is arbitrary and for the purpose of establishing a standard.

Copyright 2004, Industrial Press, Inc., New York, NYACME SCREW THREADS

Machinery's Handbook 27th EditionTable 3. General Purpose Acme Single-Start Screw Thread Data ASME/ANSI B1.5-1988IdentificationBasic DiametersThread DataNominalThreadsClasses 2G, 3G, and 4GThicknessBasicBasicLead Angle λ at BasicSizesperMajorPitchMinorat PitchHeight ofWidth ofPitch DiameteraShearStress(AllInch,aDiameter,Diameter,Diameter,Pitch,Line,Thread,Flat,Classes 2G, 3G,and 4GAreabAreacClasses)nDD2 = D − hD1 = D − 2hPt = P/2h = P/2F = 0.3707PDegMinClass 3GClass 3G1⁄4160.25000.21880.18750.062500.031250.031250.02325120.3500.02855⁄16140.31250.27680.24110.071430.035710.035710.02654420.4510.04743⁄8120.37500.33330.29170.083330.041670.041670.03094330.5450.06997⁄16120.43750.39580.35420.083330.041670.041670.03093500.6600.10221⁄2100.50000.45000.40000.100000.050000.050000.0371430.7490.12875⁄880.62500.56250.50000.125000.062500.062500.0463430.9410.20433⁄460.75000.66670.58330.166670.083330.083330.06184331.1080.28487⁄860.87500.79170.70830.166670.083330.083330.06183501.3390.4150151.00000.90000.80000.200000.100000.100000.0741431.5190.535411⁄851.12501.02500.92500.200000.100000.100000.07413331.7510.70911⁄451.25001.15001.05000.200000.100000.100000.07413101.9830.90713⁄841.37501.25001.12500.250000.125000.125000.09273392.1391.05911⁄241.50001.37501.25000.250000.125000.125000.09273192.3721.29813⁄441.75001.62501.50000.250000.125000.125000.09272482.8371.851242.00001.87501.75000.250000.125000.125000.09272263.3012.50121⁄432.25002.08331.91670.333330.166670.166670.12362553.6433.04921⁄232.50002.33332.16670.333330.166670.166670.12362364.1103.87023⁄432.75002.58332.41670.333330.166670.166670.12362214.5774.788323.00002.75002.50000.500000.250000.250000.18533194.7865.2731⁄223.50003.25003.00000.500000.250000.250000.18532485.737.50424.00003.75003.50000.500000.250000.250000.18532266.6710.1241⁄224.50004.25004.00000.500000.250000.250000.1853297.6013.13525.00004.75004.50000.500000.250000.250000.18531558.5416.53a

All other dimensions are given in inches.

b

Per inch length of engagement of the external thread in line with the minor diameter crests of the internal thread. Figures given are the minimum shear area based onmax D1 and min d2.

c

Figures given are the minimum stress area based on the mean of the minimum minor and pitch diameters of the external thread. See formulas for shear area andstress area on page1827.

Copyright 2004, Industrial Press, Inc., New York, NYACME SCREW THREADS1831

Machinery's Handbook 27th Edition1832CENTRALIZING ACME SCREW THREADSTable 4. American National Standard General Purpose Acme Single-Start Screw

Threads — Pitch Diameter Allowances ASME/ANSI B1.5-1988Nominal Size

RangeaTo andAboveIncluding03⁄165⁄167⁄169⁄1611⁄1613⁄1615⁄163⁄165⁄167⁄169⁄1611⁄1613⁄1615⁄16Allowances on External Threads

bClass 2Gc,Class 3G,Class 4G,Nominal Size

RangeaTo andAboveIncluding17⁄1619⁄1617⁄821⁄823⁄825⁄827⁄831⁄433⁄441⁄443⁄419⁄1617⁄821⁄823⁄825⁄827⁄831⁄433⁄441⁄443⁄451⁄2Allowances on External Threads

bClass 2Gc,Class 3G,Class 4G,0.008D0.00240.00400.00490.00570.00630.00690.00750.00800.00850.00890.00940.006D0.00180.00300.00370.00420.00470.00520.00560.00600.00640.00670.00700.004D0.00120.00200.00240.00280.00320.00350.00370.00400.00420.00450.00470.008D0.00980.01050.01130.01200.01260.01330.01400.01500.01600.01700.01810.006D0.00730.00790.00850.00900.00950.00990.01050.01120.01200.01270.01360.004D0.00490.00520.00570.00600.00630.00660.00700.00750.00800.00850.009111⁄1613⁄1615⁄1617⁄1611⁄1613⁄1615⁄16All dimensions in inches. It is recommended that the sizes given in Table 3 be used whenever possible.a

The values in columns for Classes 2G, 3G, and 4G are to be used for any size within the nominalsize range shown. These values are calculated from the mean of the range.

b

An increase of 10 per cent in the allowance is recommended for each inch, or fraction thereof, thatthe length of engagement exceeds two diameters.

c

Allowances for the 2G Class of thread in this table also apply to American National Standard StubAcme threads ASME/ANSI B 1.8-1988.

three-start threads, 75 per cent of these allowances; and for four-start threads, 100 per centof these same values will provide for a 0.25-16 ACME-2G thread size, 0.002, 0.003, and 0.004inch additional clearance for 2-, 3-, and 4-start threads, respectively. For a 5-2 ACME-3Gthread size the additional clearances would be 0.0091, 0.0136, and 0.0181 inch, respec-tively. GO thread plug gages and taps would be increased by these same values. To main-tain the same working tolerances on multi-start threads, the pitch diameter of the NOT GOthread plug gage would also be increased by these same multi-start threads with more than four starts, it is believed that the 100 per centallowance provided by the above procedures would be adequate as index spacing variableswould generally be no greater than on a four-start general, for multi-start threads of Classes 2G, 3G, and 4G the percentages would beapplied, usually, to allowances for the same class, respectively. However, where excep-tionally good control over lead, angle, and spacing variables would produce close to theo-retical values in the product, it is conceivable that these percentages could be applied toClass 3G or Class 4G allowances used on Class 2G internally threaded product. Also, thesepercentages could be applied to Class 4G allowances used on Class 3G internally threadedproduct. It is not advocated that any change be made in externally threaded ations for gages or tools for internal threads could cover allowance requirementsas follows:GO and NOT GO thread plug gages for: 2.875-0.4P-0.8L-ACME-2G with 50 per cent ofthe 4G internal thread lizing Acme Threads.—The three classes of Centralizing Acme threads in Amer-ican National Standard ASME/ANSI B1.5-1988, designated as 2C, 3C, and 4C, have lim-ited clearance at the major diameters of internal and external threads so that a bearing at themajor diameters maintains approximate alignment of the thread axis and prevents wedgingCopyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionCENTRALIZING ACME SCREW THREADS1833Table 5. American National Standard General Purpose Acme Single-Start Screw

Threads — Pitch Diameter Tolerances ASME/ANSI B1.5-1988Class of .,aD1⁄45⁄163⁄87⁄161⁄25⁄83⁄47⁄8Class of .,aD11⁄213⁄4221⁄421⁄223⁄4331⁄2441⁄25…hc,n4321⁄2211⁄211⁄32Gb3GDiameter Increment4G3GDiameter Increment0.006D.00300.00335.00367.00397.00424.00474.00520.00561.00600.00636.00671.007042Gb0.0028D.00140.00157.00171.00185.00198.00221.00242.00262.00280.00297.00313.00328Class of Thread3GPitch Increment0.002D.00100.00112.00122.00132.00141.00158.00173.00187.00200.00212.00224.002354G0.006D.00735.00794.00849.00900.00949.00995.01039.01122.01200.01273.01342…2Gb0.0028D.00343.00370.00396.00420.00443.00464.00485.00524.00560.00594.00626…Class of Thread3GPitch Increment0.002D.00245.00265.00283.00300.00316.00332.00346.00374.00400.00424.00447…4G111⁄811⁄413⁄hc,n.0301⁄n.00750.00802.00866.00949.01061.012250.0141⁄n.00350.00374.00404.00443.00495.005720.0101⁄n.00250.00267.00289.00316.00354.004080.0301⁄n.01500.01732.01897.02121.02449.025980.0141⁄n.00700.00808.00885.00990.01143.012120.0101⁄n.00500.00577.00632.00707.00816.008665.01342.00626.004471.03000.01400.01000For any particular size of thread, the pitch diameter tolerance is obtained by adding the diameter increment from the upper half

of the table to the pitch increment from the lower half of the table. Example: A

1⁄4-16 Acme-2G thread has a pitch diameter toler-ance of 0.00300 + 0.00750 = 0.0105 equivalent tolerance on thread thickness is 0.259 times the pitch diameter tolerance.a

For a nominal diameter between any two tabulated nominal diameters, use the diameter incrementfor the larger of the two tabulated nominal diameters.

b

Columns for the 2G Class of thread in this table also apply to American National Standard StubAcme threads, ASME/ANSI B1.8-1988 (R2001).

c

All other dimensions are given in inches.

on the flanks of the thread. An alternative series having centralizing control on the minordiameter is described on page1843. For any combination of the three classes of threadscovered in this standard some end play or backlash will result. Classes 5C and 6C are notrecommended for new ation: These three classes together with the accompanying specifications are forthe purpose of ensuring the interchangeable manufacture of Centralizing Acme threadedparts. Each user is free to select the classes best adapted to his particular needs. It is sug-gested that external and internal threads of the same class be used together for centralizingassemblies, Class 2C providing the maximum end play or backlash. If less backlash or endplay is desired, Classes 3C and 4C are provided. The requirement for a centralizing fit isthat the sum of the major diameter tolerance plus the major diameter allowance on theinternal thread, and the major diameter tolerance on the external thread shall equal or beless than the pitch diameter allowance on the external thread. A Class 2C external thread,which has a larger pitch diameter allowance than either a Class 3C or 4C, can be used inter-Copyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th Edition1834CENTRALIZING ACME SCREW THREADS0.0945P max45°Internal Thread(Screw)One-halfMinor

nce1/2

Pitch

dia.

allowanceMax

minor

dia.

of

nutMin

minor

dia.

of

nutBasic

minor

minor

dia.

of

screwMin

minor

dia.

of

screwMin

pitch

dia.

of

nutMax

pitch

dia.

of

nutMax

major

dia.

of

nutMin

major

dia.

of

nutNominal

(basic)

major

dia.

(D)Max

major

dia.

of

screwMin

major

dia.

of

screwMin

depth

of

engagementhMax

pitch

screwExternal Thread(Screw)Fig. 2. Disposition of Allowances, Tolerances, and Crest Clearances for

General Purpose Single-start Acme Threads (All Classes)changeably with a Class 2C, 3C, or 4C internal thread and fulfill this requirement. Simi-larly, a Class 3C external thread can be used interchangeably with a Class 3C or 4C internalthread, but only a Class 4C internal thread can be used with a Class 4C external Form: The thread form is the same as the General Purpose Acme Thread and isshown in Fig. 3. The formulas in Table 7 determine the basic dimensions, which are givenin Table 6 for the most generally used of Thread: The angle between the sides of the thread measured in an axial plane is29 degrees. The line bisecting this 29-degree angle shall be perpendicular to the axis of rs and Fillets: External threads have the crest corners chamfered at an angle of45 degrees with the axis to a minimum depth of P/20 and a maximum depth of P/15. Thesemodifications correspond to a minimum width of chamfer flat of 0.0707P and a maximumwidth of 0.0945P (see Table 6, columns 6 and 7).External threads for Classes 2C, 3C, and 4C may have a fillet at the minor diameter notgreater than 0.1PThread Series: A series of diameters and pitches is recommended in the Standard as pre-ferred. These diameters and pitches have been chosen to meet present needs with the few-Copyright 2004, Industrial Press, Inc., New York, NYMin

pitch

screwOne-halfMinor

nceP4Basic

pitch

dia.P4

Machinery's Handbook 27th EditionCENTRALIZING ACME SCREW THREADS1835Table 6. American National Standard Centralizing Acme Screw Thread Form —

Basic Dimensions ASME/ANSI B1.5-1988ThdsperInch,n4321⁄2211⁄211⁄3Height ofThread(Basic),h = P/20.031250.035710.041670.050000.062500.083330.100000.125000.166670.200000.250000.333330.37500Total Height

of Thread

(All ExternalThreads)hs = h +

1⁄2allowancea0.03620.04070.04670.06000.07250.09330.11000.13500.17670.21000.26000.34330.38500.510045-Deg Chamfer Crest of

External ThreadsThreadThickness(Basic),t = P/20.031250.035710.041670.050000.062500.083330.100000.125000.166670.200000.250000.333330.375000.50000MinDepth,0.05P0.00310.00360.00420.00500.00620.00830.01000.01250.01670.02000.02500.03300.03800.0500Min Width

of Chamfer

Flat,0.0707P0.00440.00500.00590.00710.00880.01190.01410.01770.02360.02830.03540.04710.05300.0707Max FilletRadius,Root ofTapped

Hole,0.06P0.00380.00380.00500.00600.00750.01000.01200.01500.02000.02400.03000.04000.04500.0600Fillet Radiusat Min orDiameterof ScrewsMax (All)0.10P0.00620.00710.00830.01000.01250.01670.02000.02500.03330.04000.05000.06670.07500.1000Pitch,P0.062500.071430.083330.100000.125000.166670.200000.250000.333330.400000.500000.666670.7500011.000000.50000All dimensions in inches. See Fig. 3.a

Allowance is 0.020 inch for 10 or less threads per inch and 0.010 inch for more than 10 threads perinch.

Fig. 3. Centralizing Acme Screw Thread FormCopyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th Edition1836CENTRALIZING ACME SCREW THREADSTable 7. Formulas for Finding Basic Dimensions of

Centralizing Acme Screw ThreadsPitch = P = 1 ÷ No. threads per inch, n:Basic thread height h = 0.5PBasic thread thickness t = 0.5PBasic flat at crest Fcn = 0.3707P + 0.259 × (minor. diameter allowance on internal threads) (internal thread)Basic flat at crest Fcs = 0.3707P − 0.259 × (pitch diameter allowance on external thread) (external thread)Frn = 0.3707P − 0.259 × (major dia. allowance on internal thread)Frs = 0.3707P − 0.259 × (minor dia. allowance on external thread — pitch dia. allowance on external thread)0.0945P Max0.0707P Min0.067P Max0.050P Minr1rNrN

= 0.06P MaxDetail of filletInternal Thread (Nut)Basic

pitch

dia.1/2

pitch

dia.

allowanceMax

minor

dia.

of

nutMin

minor

dia.

of

nutBasic

minor

minor

dia.

of

screwMin

minor

dia.

of

screwMin

pitch

dia.

of

nutMax

pitch

dia.

of

nutOne-half

minor

dia.

allowance

(nut)One-half

major

dia.

allowance

(nut)hh

–

0.05PMin

major

dia.

of

nutNominal

(basic)

major

dia.

(D)Max

major

dia.

of

screwMin

major

dia.

of

screwMin

depth

of

engagementMax

major

dia.

of

nutP4Max

pitch

dia.

of

screwMin

pitch

dia.

of

screwSymbols:P = pitchh = basic thread heightOne half minor nce (screw)rSrS

= 0.1P maxExternal Thread(Screw)Detail of optional filletFig. 4. Disposition of Allowances, Tolerances, and Crest Clearances for Centralizing

Single-Start Acme Threads—Classes 2C, 3C, and 4Cest number of items in order to reduce to a minimum the inventory of both tools and series of diameters and associated pitches is given in Table Diameters: The maximum major diameter of the external thread is basic and is thenominal major diameter for all minimum pitch diameter of the internal thread is basic for all classes and is equal tothe basic major diameter D minus the basic height of thread, h. The minimum minor diam-eter of the internal thread for all classes is 0.1P above of Engagement: The tolerances specified in this Standard are applicable tolengths of engagement not exceeding twice the nominal major Diameter Allowances: Allowances applied to the pitch diameter of the externalthread for all classes are given in Table and Minor Diameter Allowances: A minimum diametral clearance is provided atthe minor diameter of all external threads by establishing the maximum minor diameter0.020 inch below the basic minor diameter for 10 threads per inch and coarser, and 0.010inch for finer pitches and by establishing the minimum minor diameter of the internalthread 0.1P greater than the basic minor ght 2004, Industrial Press, Inc., New York, NY0.05PP445°Detail of chamfer

Machinery's Handbook 27th EditionCENTRALIZING ACME SCREW THREADS1837Table 8a. American National Standard Centralizing Acme Single-Start Screw

Threads — Formulas for Determining Diameters ASME/ANSI B1.5-1988D = Nominal Size or Diameter in InchesP = Pitch = 1 ÷ Number of Threads per InchNo.123456Classes 2C, 3C, and 4C External Threads (Screws)Major Dia., Max = D (Basic).Major Dia., Min = D minus tolerance from Table 12, columns 7, 8, or Dia., Max = Int. Pitch Dia., Min (Formula 9) minus allowance from the appropri-ate Class 2C, 3C, or 4C column of Table Dia., Min = Ext. Pitch Dia., Max (Formula 3) minus tolerance from Table Dia., Max = D minus P minus allowance from Table 12, column Dia., Min = Ext. Minor Dia., Max (Formula 5) minus 1.5 × Pitch Dia. tolerance

from Table s 2C, 3C, and 4C Internal Threads (Nuts)Major Dia., Min = D plus allowance from Table 12, column Dia., Max = Int. Major Dia., Min (Formula 7) plus tolerance from Table 12, col-umns 7, 9, or Dia., Min = D minus P/2 (Basic).Pitch Dia., Max = Int. Pitch Dia., Min (Formula 9) plus tolerance from Table Dia., Min = D minus Dia., Max = Int. Minor Dia., Min (Formula 11) plus tolerance from Table 12,

column 6.789101112A minimum diametral clearance at the major diameter is obtained by establishing theminimum major diameter of the internal thread 0.001D above the basic major allowances are shown in Table and Minor Diameter Tolerances: The tolerances on the major and minor diame-ters of the external and internal threads are listed in Table 12 and are based upon the formu-las given in the column increase of 10 per cent in the allowance is recommended for each inch or fractionthereof that the length of engagement exceeds two information on gages for Centralizing Acme threads the Standard ASME/ANSI B1.5should be Diameter Tolerances: Pitch diameter tolerances for Classes 2C, 3C and 4C for var-ious practicable combinations of diameter and pitch are given in Table 11. The ratios of thepitch diameter tolerances of Classes 2C, 3C, and 4C are 3.0, 1.4, and 1, ation of Tolerances: The tolerances specified are such as to insure interchange-ability and maintain a high grade of product. The tolerances on the diameters of internalthreads are plus, being applied from the minimum sizes to above the minimum sizes. Thetolerances on the diameters of external threads are minus, being applied from the maxi-mum sizes to below the maximum sizes. The pitch diameter tolerances for an external orinternal thread of a given class are the sameLimiting Dimensions: Limiting dimensions for Centralizing Acme threads in the pre-ferred series of diameters and pitches are given in Tables 8b and 8c. These limits are basedon the formulas in Table combinations of pitch and diameter other than those in the preferred series the formu-las in Tables 8b and 8c and the data in the tables referred to therein make it possible toreadily determine the limiting dimension ght 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionTable 8b. Limiting Dimensions of American National Standard Centralizing Acme Single-Start Screw Threads, Classes 2C, 3C, and 4C ASME/ANSI B1.5-19881838Nominal Diameter, D1⁄25⁄83⁄47⁄8111⁄811⁄413⁄811⁄2Threads per Incha1086655544Limiting DiametersExternal ThreadsClasses 2C, 3C, and 4C, Major DiameterMax0.50000.62500.75000.87501.00001.12501.25001.37501.5000Class 2C, Major DiameterMin0.49750.62220.74700.87170.99651.12131.24611.37091.4957Class 3C, Major DiameterMin0.49890.62380.74870.87360.99851.12341.24831.37321.4982Class 4C, Major DiameterMin0.49930.62420.74910.87410.99901.12391.24891.37381.4988Classes 2C, 3C, and 4C, Minor DiameterMax0.38000.48000.56330.68830.78000.90501.03001.10501.2300Class 2C, Minor DiameterMin0.35940.45700.53710.66150.75090.87530.99981.07191.1965Class 3C, Minor DiameterMin0.37040.46930.55110.67580.76640.89121.01591.08961.2144Class 4C, Minor DiameterMin0.37310.47230.55460.67940.77030.89511.01991.09401.2188Class 2C, Pitch Diameter{Max0.44430.55620.65980.78420.89201.01651.14111.24061.3652Min0.43060.54080.64240.76630.87260.99671.12101.21861.3429Class 3C, Pitch Diameter{Max0.44580.55780.66150.78610.89401.01861.14331.24301.3677Min0.43940.55060.65340.77780.88491.00941.13391.23271.3573Class 4C, Pitch Diameter{Max0.44720.55930.66320.78800.89601.02081.14551.24531.3701Min0.44260.55420.65740.78200.88951.01421.13881.23801.3627Internal ThreadsClasses 2C, 3C, and 4C,Major DiameterMin0.50070.62580.75090.87591.00101.12611.25111.37621.5012Classes 2C and 3C,Major DiameterMax0.50320.62860.75390.87921.00451.12981.25501.38031.5055Class 4C, Major DiameterMax0.50210.62740.75260.87781.00300.12821.25331.37851.5036Classes 2C, 3C, and 4C, Min0.41000.51250.60000.72500.82000.94500.07001.15001.2750Minor Diameter{Max0.041500.51870.60830.73330.83000.95501.08001.16251.2875Class 2C, Pitch Diameter{Min0.45000.56250.66670.79170.90001.02501.15001.25001.3750Max0.46370.57790.68410.80960.91941.04481.17011.27201.3973Class 3C, Pitch Diameter{Min0.45000.56250.66670.79170.90001.02501.15001.25001.3750Max0.45640.56970.67480.80000.90911.03421.15941.26031.3854Class 4C, Pitch Diameter{Min0.45000.56250.66670.79170.90001.02501.15001.25001.3750Max0.45460.56760.67250.79770.90651.03161.15671.25731.3824Copyright 2004, Industrial Press, Inc., New York, NYCENTRALIZING ACME SCREW THREADS

Machinery's Handbook 27th EditionTable 8c. Limiting Dimensions of American National Standard Centralizing Acme Single-Start Screw Threads, Classes 2C, 3C, and 4C ASME/ANSI B1.5-1988Nominal Diameter, D13⁄4221⁄421⁄223⁄4331⁄21 2441⁄25Threads per Incha4433322222Limiting DiametersExternal ThreadsClasses 2C, 3C, and 4C, Major DiameterMax1.75002.00002.25002.50002.75003.00003.50004.00004.50005.0000Class 2C, Major DiameterMin1.74541.99512.24482.49452.74422.99393.49353.99304.49264.9922Class 3C, Major DiameterMin1.74801.99792.24782.49762.74752.99743.49723.99704.49684.9966Class 4C, Major DiameterMin1.74871.99862.24852.49842.74832.99833.49813.99804.49794.9978Classes 2C, 3C, and 4C, Minor DiameterMax1.48001.73001.89672.14672.39672.48002.98003.48003.98004.4800Class 2C, Minor DiameterMin1.44561.69481.85722.10652.35582.43262.93143.43023.92914.4281Class 3C, Minor DiameterMin1.46401.71361.87832.12792.37762.45792.95743.45683.95634.4558Class 4C, Minor DiameterMin1.46851.71831.88352.13332.38312.46422.96383.46343.96314.4627Class 2C, Pitch Diameter{Max1.61451.86372.07132.32072.57002.73603.23503.73404.23304.7319Min1.59161.84022.04502.29392.54272.70443.20263.70084.19914.6973Class 3C, Pitch Diameter{Max1.61711.86652.07432.32382.57342.73953.23883.73804.23734.7364Min1.60641.85552.06202.31132.56072.72483.22373.72254.22154.7202Class 4C, Pitch Diameter{Max1.61981.86932.07732.32702.57672.74303.24253.74204.24154.7409Min1.61221.86152.06852.31812.56762.73253.23173.73094.23024.7294Internal ThreadsClasses 2C, 3C, and 4C,Major DiameterMin1.75132.00142.25152.50162.75173.00173.50194.00204.50215.0022Classes 2C and 3C,Major DiameterMax1.75592.00632.25672.50712.75753.00783.50844.00904.50955.0100Class 4C, Major DiameterMax1.75392.00422.25452.50482.75503.00523.50564.00604.50635.0067Classes 2C, 3C, and 4C,Min1.52501.77501.95002.20002.45002.55003.05003.55004.05004.5500Minor Diameter{Max1.53751.78751.96672.21672.46672.57503.07503.57504.07504.5750Class 2C, Pitch Diameter{Min1.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Max1.64791.89852.10962.36012.61062.78163.28243.78324.28394.7846Class 3C, Pitch Diameter{Min1.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Max1.63571.88602.09562.34582.59602.76473.26513.76554.26584.7662Class 4C Pitch Diameter{Min1.62501.87502.08332.33332.58332.75003.25003.75004.25004.7500Max1.63261.88282.09212.34222.59242.76053.26083.76114.26134.7615a

All other dimensions are in inches. The selection of threads per inch is arbitrary and for the purpose of establishing a standard.

Copyright 2004, Industrial Press, Inc., New York, NYCENTRALIZING ACME SCREW THREADS1839

Machinery's Handbook 27th EditionTable 9. American National Standard Centralizing Acme Single-Start Screw Thread Data ASME/ANSI B1.5-1988Identification1840DiametersThread DataThreadsCentralizing, Classes 2C, 3C, and 4CBasicLead Angle λ at Basic Pitch DiameteraNominalperBasic MajorPitchMinorThickness atHeight ofBasic WidthCentralizing Classes 2C, 3C, and 4C,

SizesInch,aDiameter,Diameter,Diameter,

of Flat,(All Classes)nDD2 = (D − h)DPitch,Pitch Line,Thread,1 = (D − 2h)Pt = P/2h = P/2F = 0.3707PDegMin1⁄4160.25000.21880.18750.062500.031250.031250.02325125⁄16140.31250.27680.24110.071430.035710.035710.02654423⁄8120.37500.33330.29170.083330.041670.041670.03094337⁄16120.43750.39580.35420.083330.041670.041670.03093501⁄2100.50000.45000.40000.100000.050000.050000.0371435⁄880.62500.56250.50000.125000.062500.062500.0463433⁄460.75000.66670.58330.166670.083330.083330.06184337⁄860.87500.79170.70830.166670.083330.083330..00000.90000.80000.200000.100000.100000.07414311⁄851.12501.02500.92500.200000.100000.100000.074133311⁄451.25001.15001.05000.200000.100000.100000.074131013⁄841.37501.25001.12500.250000.125000.125000.092733911⁄241.50001.37501.25000.250000.125000.125000.092731913⁄441.75001.62501.50000.250000.125000.125000..00001.87501.75000.250000.125000.125000.092722621⁄432.25002.08331.91670.333330.166670.166670.123625521⁄232.50002.33332.16670.333330.166670.166670.123623623⁄432.75002.58332.41670.333330.166670.166670.1236221323.00002.75002.50000.500000.250000.250000.185331931⁄223.50003.25003.00000.500000.250000.250000.1853248424.00003.75003.50000.500000.250000.250000.185322641⁄224.50004.25004.00000.500000.250000.250000.185329525.00004.75004.50000.500000.250000.250000.1853155a

All other dimensions are given in inches.

Copyright 2004, Industrial Press, Inc., New York, NYCENTRALIZING ACME SCREW THREADS

Machinery's Handbook 27th EditionCENTRALIZING ACME SCREW THREADS1841Table 10. American National Standard Centralizing Acme Single-Start Screw

Threads — Pitch Diameter Allowances ASME/ANSI B1.5-1988Nominal Size

RangeaToandAboveIncluding3⁄0163⁄165⁄167⁄169⁄1611⁄1613⁄1615⁄1611⁄1613⁄1615⁄165⁄167⁄169⁄1611⁄1613⁄1615⁄1611⁄1613⁄1615⁄1617⁄16Allowances on External ThreadsbCentralizingClass 2C,Class 3C,Class 4C,Nominal Size

RangeaToandAboveIncluding17⁄1619⁄1617⁄821⁄823⁄825⁄827⁄831⁄433⁄441⁄443⁄419⁄1617⁄821⁄823⁄825⁄827⁄831⁄433⁄441⁄443⁄451⁄2Allowances on External ThreadsbCentralizingClass 2C,Class 3C,Class 4C,0.008D0.00240.00400.00490.00570.00630.00690.00750.00800.00850.00890.00940.006D0.00180.00300.00370.00420.00470.00520.00560.00600.00640.00670.00700.004D0.00120.00200.00240.00280.00320.00350.00370.00400.00420.00450.00470.008D0.00980.01050.01130.01200.01260.01330.01400.01500.01600.01700.01810.006D0.00730.00790.00850.00900.00950.00990.01050.01120.01200.01270.01360.004D0.00490.00520.00570.00600.00630.00660.00700.00750.00800.00850.0091All dimensions are given in inches.

It is recommended that the sizes given in Table 9 be used whenever possible.a

The values in columns for Classes 2C, 3C, and 4C are to be used for any size within the nominalsize range columns. These values are calculated from the mean of the range.

b

An increase of 10 per cent in the allowance is recommended for each inch, or fraction thereof, thatthe length of engagement exceeds two diameters.

Table 11. American National Standard Centralizing Acme Single-Start Screw

Threads — Pitch Diameter Tolerances ASME/ANSI .,aD1⁄45⁄163⁄87⁄161⁄25⁄83⁄47⁄8Class of Thread and Diameter .,aD11⁄213⁄4221⁄421⁄223⁄4331⁄2441⁄25…Class of Thread and Diameter Increment2C3C4C0.006D.00735.00794.00849.00900.00949.00995.01039.01122.01200.01273.01342…0.0028D.00343.00370.00396.00420.00443.00464.00485.00524.00560.00594.00626…0.002D.00245.00265.00283.00300.00316.00332.00346.00374.00400.00424.00447…111⁄811⁄413⁄8Class of Thread and Pitch IncrementClass of Thread and Pitch .2C3C4C2C3C4CperperInch,Inch,0.0301⁄n0.0141⁄n0.0101⁄n0.0301⁄n0.0141⁄n0.0101⁄nnn16.00750.00350.002504.01500.00700.0050014.00802.00374.002673.01732.00808.0057712.00866.00404.00289.01897.00885.0063221⁄210.00949.00443.003162.02121.00990.00707.02449.01143.008168.01061.00495.0035411⁄2.02598.01212.008666.01225.00572.0040811⁄35.01342.00626.004471.03000.01400.01000All dimensions are given in any particular size of thread, the pitch diameter tolerance is obtained by adding the diameter increment from the upper half

of the table to the pitch increment from the lower half of the table. Example: A 0.250-16-ACME-2C thread has a pitch diameter

tolerance of 0.00300 + 0.00750 = 0.0105 equivalent tolerance on thread thickness is 0.259 times the pitch diameter tolerance.a

For a nominal diameter between any two tabulated nominal diameters, use the diameter incrementfor the larger of the two tabulated nominal diameters.

Copyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionTable 12. American National Standard Centralizing Acme Single-Start Screw Threads —

Tolerances and Allowances for Major and Minor Diameters ASME/ANSI B1.5-19881842Allowance From Basic Major andMinor Diameters (All Classes)Tolerance on Major Diameter Plus on Internal, Minus on External ThreadsInternal ThreadToleranceClass 2CClass 3CClass 4CMinor Diam,

dMajor Diam,

eon Minor Diam,

b, cExternal andExternalInternalExternalInternalThdsaAll External(PlusMinorAll InternalInternal Threads,Thread,Thread,Thread,Thread,SizeperThreadsThreads,(Nom.)Inch(Minus)0.0010D)Diam,

d(Plus 0.1P)(Plus 0.05P)0.0035D0.0015D0.0035D0.0010D0.0020D1⁄4160.0100.00050.00620.00500.00170.00070.00170.00050.00105⁄16140.0100.00060.00710.00500.00200.00080.00200.00060.00113⁄8120.0100.00060.00830.00500.00210.00090.00210.00060.00127⁄16120.0100.00070.00830.00500.00230.00100.00230.00070.00131⁄2100.0200.00070.01000.00500.00250.00110.00250.00070.00145⁄880.0200.00080.01250.00620.00280.00120.00280.00080.00163⁄460.0200.00090.01670.00830.00300.00130.00300.00090.00177⁄860.0200.00090.01670.00830.00330.00140.00330.00090.0019150.0200.00100.02000.01000.00350.00150.00350.00100.002011⁄850.0200.00110.02000.01000.00370.00160.00370.00110.002111⁄450.0200.00110.02000.01000.00390.00170.00390.00110.002213⁄840.0200.00120.02500.01250.00410.00180.00410.00120.002311⁄240.0200.00120.02500.01250.00430.00180.00430.00120.002413⁄440.0200.00130.02500.01250.00460.00200.00460.00130.0026240.0200.00140.02500.01250.00490.00210.00490.00140.002821⁄430.0200.00150.03330.01670.00520.00220.00520.00150.003021⁄230.0200.00160.03330.01670.00550.00240.00550.00160.003223⁄430.0200.00170.03330.01670.00580.00250.00580.00170.0033320.0200.00170.05000.02500.00610.00260.00610.00170.003531⁄220.0200.00190.05000.02500.00650.00280.00650.00190.0037420.0200.00200.05000.02500.00700.00300.00700.00200.004041⁄220.0200.00210.05000.02500.00740.00320.00740.00210.0042520.0200.00220.05000.02500.00780.00340.00780.00220.0045a

All other dimensions are given in inches. Intermediate pitches take the values of the next coarser pitch listed. Values for intermediate diameters should be calculatedfrom the formulas in column headings, but ordinarily may be interpolated.

b

To avoid a complicated formula and still provide an adequate tolerance, the pitch factor is used as a basis, with the minimum tolerance set at 0.005 in.

c

Tolerance on minor diameter of all external threads is 1.5 × pitch diameter tolerance.

d

The minimum clearance at the minor diameter between the internal and external thread is the sum of the values in columns 3 and 5.

e

The minimum clearance at the major diameter between the internal and external thread is equal to column 4.

Copyright 2004, Industrial Press, Inc., New York, NYCENTRALIZING ACME SCREW THREADS

Machinery's Handbook 27th EditionSTUB ACME SCREW THREADS1843Designation of Centralizing Acme Threads.—The following examples are given toshow how these Acme threads are designated on drawings, in specifications, and on toolsand gages:Example, 1.750-6-ACME-4C:Indicates a Centralizing Class 4C Acme thread of 1.750-inch major diameter, 0.1667-inch pitch, single thread, e, 1.750-6-ACME-4C-LH:Indicates the same thread e, 2.875-0.4P-0.8L-ACME-3C (Two Start):Indicates a Centralizing Class 3CAcme thread with 2.875-inch major diameter, 0.4-inch pitch, 0.8-inch lead, double thread,e, 2.500-0.3333P-0.6667L-ACME-4C (Two Start):Indicates a CentralizingClass 4C Acme thread with 2.500-inch nominal major diameter (basic major diameter2.500 inches), 0.3333-inch pitch, 0.6667-inch lead, double thread, right-hand. The samethread left-hand would have LH at the end of the Centralizing Threads—Alternative Series with Minor Diameter CentralizingControl.—When Acme centralizing threads are produced in single units or in very smallquantities (and principally in sizes larger than the range of commercial taps and dies)where the manufacturing process employs cutting tools (such as lathe cutting), it may beeconomically advantageous and therefore desirable to have the centralizing control of themating threads located at the minor ularly under the above-mentioned type of manufacturing, the two advantages citedfor minor diameter centralizing control over centralizing control at the major diameters ofthe mating threads are: 1) Greater ease and faster checking of machined thread dimen-sions. It is much easier to measure the minor diameter (root) of the external thread and themating minor diameter (crest or bore) of the internal thread than it is to determine the majordiameter (root) of the internal thread and the major diameter (crest or turn) of the externalthread; and 2) better manufacturing control of the machined size due to greater ease the event that minor diameter centralizing is necessary, recalculate all thread dimen-sions, reversing major and minor diameter allowances, tolerances, radii, and an National Standard Stub Acme Threads.—This American National Stan-dard ASME/ANSI B1.8-1988 (R2001) provides a Stub Acme screw thread for thoseunusual applications where, due to mechanical or metallurgical considerations, a coarse-pitch thread of shallow depth is required. The fit of Stub Acme threads corresponds to theClass 2G General Purpose Acme thread in American National Standard ANSI a fit having less backlash, the tolerances and allowances for Classes 3G or 4G GeneralPurpose Acme threads may be Form: The thread form and basic formulas for Stub Acme threads are given onpage1826 and the basic dimensions in Table nces and Tolerances: The major and minor diameter allowances for Stub Acmethreads are the same as those given for General Purpose Acme threads on diameter allowances for Stub Acme threads are the same as for Class 2G GeneralPurpose Acme threads and are given in Table 4. Pitch diameter tolerances for Stub Acmethreads are the same as for Class 2G General Purpose Acme threads given in Table ng Dimensions: Limiting dimensions of American Standard Stub Acme threadsmay be determined by using the formulas given in Table 14a, or directly from Table diagram below shows the limits of size for Stub Acme Series: A preferred series of diameters and pitches for General Purpose Acmethreads (Table 15) is recommended for Stub Acme ght 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th Edition1844ALTERNATIVE STUB ACME SCREW THREADSTable 13. American National Standard Stub Acme Screw Thread Form — Basic

Dimensions ASME/ANSI B1.8-1988 (R2001)han65431⁄2321⁄2211⁄211⁄31Height ofThread(Basic),0.3P0.018750.021430.025000.030000.033330.037500.042850.050000.060000.075000.085710.100000.120000.150000.200000.225000.30000TotalHeight ofThread,0.3P +

1⁄2allowanceb0.02380.02640.03000.04000.04330.04750.05290.06000.07000.08500.09570.11000.13000.16000.21000.23500.3100Width of FlatThreadThickness(Basic),P/20.031250.035710.041670.050000.055560.062500.071430.083330.100000.125000.142860.166670.200000.250000.333330.375000.50000Crest ofInternalThread(Basic),0.4224P0.02640.03020.03520.04220.04690.05280.06030.07040.08450.10560.12070.14080.16900.21120.28160.31680.4224Root of InternalThread,0.4224P −0.259

×allowanceb0.02380.02760.03260.03700.04170.04760.05510.06520.07930.10040.11550.13560.16380.20600.27640.31160.4172Pitch,P = 1/n0.062500.071430.083330.100000.111110.125000.142860.166670.200000.250000.285710.333330.400000.500000.666670.750001.00000a

All other dimensions in inches. See Fig. 1, page1826.

b

Allowance is 0.020 inch for 10 or less threads per inch and 0.010 inch for more than 10 threads perinch.

Table 14a. American National Standard Stub Acme Single-Start Screw Threads —

Formulas for Determining Diameters ASME/ANSI B1.8-1988 (R2001)D = Basic Major Diameter and Nominal Size in InchesD2 = Basic Pitch Diameter = D − 0.3PD1 = Basic Minor Diameter = D − 0.6PNo.123456External Threads (Screws)Major Dia., Max = Dia., Min. = D minus Dia., Max. = D2 minus allowance from the appropriate Class 2G column, Table Dia., Min. = Pitch Dia., Max. (Formula 3) minus Class 2G tolerance from Table Dia., Max. = D1 minus 0.020 for 10 threads per inch and coarser and 0.010 for finer

Dia., Min. = Minor Dia., Max. (Formula 5) minus Class 2G pitch diameter tolerance

from Table al Threads (Nuts)Major Dia., Min. = D plus 0.020 for 10 threads per inch and coarser and 0.010 for finer

Dia., Max.= Major Dia., Min. (Formula 7) plus Class 2G pitch diameter tolerance

from Table Dia., Min. = D2 = D − 0.3PPitch Dia., Max. = Pitch Dia., Min. (Formula 9) plus Class 2G tolerance from Table Dia., Min. = D1 = D − 0.6PMinor Dia., Max = Minor Dia., Min. (Formula 11) plus 0.05P.789101112Copyright 2004, Industrial Press, Inc., New York, NY

Machinery's Handbook 27th EditionTable 14b. Limiting Dimensions for American National Standard Stub Acme Single-Start Screw Threads ASME/ANSI B1.8-1988 (R2001)Nominal Diameter, DThreads per InchaLimiting DiametersMajor Dia.{{{Max (D)MinMaxMinMaxMinMinMaxMinMaxMinMax0.25000.24690.22720.21670.20240.19190.26000.27050.23120.24170.21250.215611⁄241.50001.48751.41521.39291.33001.30771.52001.54230.31250.30890.28710.27570.25970.24830.32250.33390.29110.30250.26960.273213⁄441.75001.73751.66451.64161.58001.55711.77001.79290.37500.37080.34510.33280.31500.30270.38500.39730.35000.36230.32500.3292242.00001.98751.91371.89021.83001.80652.02002.04350.43750.43330.40760.39500.37750.36490.44750.46010.41250.42510.38750.391721⁄432.25002.23332.13802.11172.03002.00372.27002.29630.50000.49500.46430.45060.42000.40630.52000.53370.47000.48370.44000.445021⁄232.50002.48332.38742.36062.28002.25322.52002.54681⁄45⁄163⁄87⁄161⁄25⁄83⁄47⁄8660.87500.86670.81750.79960.75500.73710.89500.91290.82500.84290.77500.7833323.00002.97502.83602.80442.68002.64843.02003.0516151.00000.99000.93200.91260.86000.84061.02001.03940.94000.95940.88000.890031⁄223.50003.47503.33503.30263.18003.14763.52003.552411⁄851.12501.11501.05651.03670.98500.96521.14501.16481.06501.08481.00501.0150424.00003.97503.83403.80083.68003.64684.02004.053211⁄451.25001.24001.18111.16101.11001.08991.27001.29011.19001.21011.13001.140041⁄224.50004.47504.33304.29914.18004.14614.52004.553913⁄841.37501.36251.29061.26861.20501.18301.39501.41701.30001.32201.22501.2375525.00004.97504.83194.79734.68004.64545.02005.0546External Threads0.62500.75000.61880.74170.58120.69310.56580.67570.53000.63000.51460.6126Internal Threads0.64500.77000.66040.78740.58750.70000.60290.71740.55000.65000.55620.658323⁄43External Threads2.75002.73332.63672.60942.53002.5027Internal Threads2.77002.7973ALTERNATIVE STUB ACME SCREW THREADSMajor Dia.{{{Nominal Diameter, DThreads per InchaLimiting DiametersMajor Dia.{{{Max (D)MinMaxMinMaxMinMinMaxMajor Dia.{Pitch Dia.{Min1.42501.67501.92502.15002.40002.65002.85003.35003.85004.35004.8500Max1.44731.69791.94852.17632.42682.67732.88163.38243.88324.38394.8846Minor Dia.{Min1.35001.60001.85002.05002.30002.55002.70003.20003.70004.20004.7000Max1.36251.61251.86252.06672.31672.56672.72503.22503.72504.22504.7250a

All other dimensions are given in inches.

Copyright 2004, Industrial Press, Inc., New York, NY1845

Machinery's Handbook 27th Edition1846ALTERNATIVE CENTRALIZING ACME SCREW THREADSP′Internal Thread(Nut)One-halfmajor

nceBasic thickness of thread, P/21/2

Pitch

dia.

allowanceMax

minor

dia.

of

nutMin

minor

dia.

of

nutBasic

minor

minor

dia.

of

screwMin

minor

dia.

of

screwMin

minor

dia.

of

screwMin

pitch

dia.

of

nutBasic

pitch

dia.0.15PMin

depth

ofengagementMax

major

dia.

of

nutMin

major

dia.

of

nutNominal

(basic)

major

dia.

(D)Max

major

dia.

of

screwMin

major

dia.

of

screwhMax

pitch

screwMin

pitch

screwExternal Thread(Screw)Limits of Size, Allowances, Tolerances, and Crest Clearances forAmerican National Standard Stub Acme ThreadsStub Acme Thread Designations.—The method of designation for Standard Stub Acmethreads is illustrated in the following examples: 0.500-20 Stub Acme indicates a

1⁄2-inchmajor diameter, 20 threads per inch, right hand, single thread, Standard Stub Acme designation 0.500-20 Stub Acme-LH indicates the same thread except that it is ative Stub Acme Threads.—Since one Stub Acme thread form may not meet therequirements of all applications, basic data for two of the other commonly used forms areincluded in the appendix of the American Standard for Stub Acme Threads. These so-called Modified Form 1 and Modified Form 2 threads utilize the same tolerances andallowances as Standard Stub Acme threads and have the same major diameter and basicthread thickness at the pitchline (0.5P). The basic height of Form 1 threads, h, is 0.375P;for Form 2 it is 0.250P. The basic width of flat at the crest of the internal thread is 0.4030Pfor Form 1 and 0.4353P for Form pitch diameter and minor diameter for Form 1 threads will be smaller than similarvalues for the Standard Stub Acme Form and for Form 2 they will be larger owing to thedifferences in basic thread height h. Therefore, in calculating the dimensions of Form 1 andForm 2 threads using Formulas 1 through 12 in Table 14a, it is only necessary to substitutethe following values in applying the formulas: For Form 1, D2 = D − 0.375P, D1 = D −0.75P; for Form 2, D2 = D − 0.25P, D1 = D − Designation: These threads are designated in the same manner as Standard StubAcme threads except for the insertion of either M1 or M2 after “Acme.” Thus, 0.500-20Stub Acme M1 for a Form 1 thread; and 0.500-20 Stub Acme M2 for a Form 2 60-Degree Stub Thread.—Former American Standard B1.3-1941 included a60-degree stub thread for use where design or operating conditions could be better satisfiedby the use of this thread, or other modified threads, than by Acme threads. Data for 60-Degree Stub thread form are given in the accompanying ght 2004, Industrial Press, Inc., New York, NYOne-halfmajor

nce0.15P

Machinery's Handbook 27th EditionTable 15. Stub Acme Screw Thread Data ASME/ANSI B1.8-1988 (R2001)IdentificationThreadsper Inch,an2MajorDiameter,D0.25000.31250.37500.43750.50000.62500.75000.87501.00001.12501.25001.37501.50001.75002.00002.25002.50002.75003.0000Basic DiametersPitchDiameter,D2 = D − h0.23120.29110.35000.41250.47000.58750.70000.82500.94001.06501.19001.30001.42501.67501.92502.15002.40002.65002.8500MinorDiameter,D1 = D − 2h0.21250.26960.32500.38750.44000.55000.65000.77500.88001.00501.13001.22501.35001.60001.85002.05002.30002.55002.7000Thread Thicknessat Pitch Line,t = P/20.031250.035720.041670.041670.050000.062500.083330.083330.100000.100000.100000.125000.125000.125000.125000.166670.166670.166670.25000Thread DataBasic ThreadHeight,h = 0.3P0.018750.021430.025000.025000.030000.037500.050000.050000.060000.060000.060000.075000.075000.075000.075000.100000.100000.100000.15000Basic Widthof Flat,0.4224P0.02640.03020.03520.03520.04220.05280.07040.07040.08450.08450.08450.10560.10560.10560.10560.14080.14080.14080.2112Lead Angleat

Basic

Pitch DiameterDeg4443334333333222223MinNominalSizes1⁄45⁄163⁄87⁄161⁄25⁄83⁄47⁄8Pitch,P0.062500.071430.083330.083330.100000.125000.166670.166670.200000.200000.200000.250000.250000.250000.250000.333330.333330.333330.50000ALTERNATIVE CENTRALIZING ACME SCREW

5428222543812111⁄811⁄413⁄811⁄213⁄4221⁄421⁄223⁄4331⁄223.50003.35003.20000.500000.250000.150000.2112243424.00003.85003.70000.500000.250000.150000.211222241⁄224.50004.35004.20000.500000.250000.150000.211226525.00004.85004.70000.500000.250000.150000.2112153a

All other dimensions are given in inches.

Copyright 2004, Industrial Press, Inc., New York, NY1847

Machinery's Handbook 27th Edition1848ALTERNATIVE CENTRALIZING ACME SCREW THREADS60-Degree Stub ThreadA clearance of at least 0.02 × pitch is added to depth h to produce extra depth, thus avoid-ing interference with threads of mating part at minor or major thread thickness at pitch line = 0.5 × pitch p; basic depth h = 0.433 × pitch; basicwidth of flat at crest = 0.25 × pitch; width of flat at root of screw thread = 0.227 × pitch;basic pitch diameter = basic major diameter − 0.433 × pitch; basic minor diameter = basicmajor diameter − 0.866 × Thread.—The square thread is so named because the section is square, the depth,in the case of a screw, being equal to the width or one-half the pitch. The thread groove in asquare-threaded nut is made a little greater than one-half the pitch in order to provide aslight clearance for the screw; hence, the tools used for threading square-threaded taps area little less in width at the point than one-half the pitch. The pitch of a square thread is usu-ally twice the pitch of an American Standard thread of corresponding diameter. The squarethread has been superseded quite largely by the Acme form which has several ACME SCREW THREADS.10-Degree Modified Square Thread: The included angle between the sides of the threadis 10 degrees (see accompanying diagram). The angle of 10 degrees results in a threadwhich is the practical equivalent of a “square thread,” and yet is capable of economical pro-duction. Multiple thread milling cutters and ground thread taps should not be specified formodified square threads of the larger lead angles without consulting the cutting tool nce (See Note)0.25pp2Nut0.4563p5˚p2h0.25p1Pitch

2Diameter

AllowanceGScrewClearance (See Note)In the following formulas, D = basic major diameter; E = basic pitch diameter; K = basicminor diameter; p = pitch; h = basic depth of thread on screw depth when there is no clear-ance between root of screw and crest of thread on nut; t = basic thickness of thread at pitchline; F = basic width of flat at crest of screw thread; G = basic width of flat at root of screwthread; C = clearance between root of screw and crest of thread on nut: E = D − 0.5p; K = D− p; h = 0.5p (see Note); t = 0.5p; F = 0.4563p; G = 0.4563p − (0.17 × C).

Note: A clearance should be added to depth h to avoid interference with threads of matingparts at minor or major ght 2004, Industrial Press, Inc., New York, NY