英美螺纹资料

Thread

1 Definition

The diameters, threads per inch (TPI) and thread pitch, etc. are necessary to completely

identify a thread. In a shop, specialty gauges are required to accurately gauge or identify

threads. In the field, in the absence of these gauges, thread "leaf" gauges can be used to

identify the "Threads Per Inch" (TPI) and the thread pitch. On threads you have determined to

be straight threads, a caliper can be used to measure the "Outside Diameter of the Male"

(ODM) or the "Inside Diameter of the Female" (IDF). A caliper can also be used to take

measurements of tapered thread diameters. However, these are more difficult to define

because of the taper. Fortunately, there are few tapered threads to deal with and these can

usually be identified from the nominal ODM and the TPI.

However, identifying the thread may not fully identify what is needed in a mating

fitting. The application is the primary limiting factor on the thread type used.

We offer products with a wide variety of threads used with hose, pipe and

hydraulics.

When attempting to choose a fitting, it is always advisable to first identify the

thread to which it must connect. This may entail checking with a fitting or

equipment manufacturer.

The fire hose thread specifications for some local municipal fire

equipment and hydrants may vary according to local specifications. These

can generally be most easily identified by contacting the local fire department

responsible for the hydrant. The most common thread used on fire equipment is

National Standard Thread (NST), also known as National Hose thread (NH).

When it is not possible to identify the thread:

• 1)Determine the number of threads per inch by measuring the distance

from peak of thread to peak of thread across the largest number of

whole threads. Then divide the number of threads by the measurement.

(This will provide the TPI).

• 2) Check to see if the thread is straight or tapered.

a) Straight Threads

Measure the "Outside Diameter of the Male" (ODM) or the "Inside

Diameter of the Female" (IDF), from peak of thread to peak of thread.

b) Tapered Threads

Measure the "Outside Diameter of the Male" (ODM) at the large end

and the small end, or the "Inside Diameter of the Female" (IDF) at the

large end and the small end, from peak of thread to peak of thread.

Then measure the Outside Diameter (OD) of the unthreaded pipe.

Once the application and these two pieces of information have been

determined, the thread can generally be determined. When in doubt, contact

the manufacturer.

Straight Thread

Male

Female

Tapered Thread

Male

Female

Threading Information

Abbreviation System Name

British Standard Pipe

Parallel

Compatibility

Male BSPP with Female BSPP

BSPP

Female BSPP with Male BSPP

Female BSPP with Male BSPTr

Male BSPTr with Female BSPTr

British Standard Pipe

Taper

Male BSPTr with Female BSPP

Female BSPTr with Male BSPTr

Female BSPTr not compatible

with Male BSPP

1"Male NH (NST) with 1" Female

NH (NST)

American Standard Fire

Hose Thread (1" National

CHT

Hose Thread is Chemical

Hose Thread, also known

as Booster Hose Thread)1" Female NH (NST) with 1" Male

NH (NST)

1" Thread is used on both ¾"

hose & 1" hose.

Not compatible with other

systems

Male GHT with Female GHT

Female GHT with Male GHT

GHT Garden Hose Thread

Thread is the same for all size

hose.

Not compatible with other

systems

Generic name for Straight Pipe

IPS Iron Pipe Straight ThreadThread

See NPSH for compatibility

JIC Joint Industrial CommitteeUsed with other mating JIC

threads

Male NH (NST) with Female NH

American Standard Fire

NH

or

NST

Hose Coupling Thread

(National Hose thread also

known as National

Standard Thread

(NST)

Female NH (NST) with Male NH

(NST)

Not compatible with other

systems

Thread pitch and diameters of fire

Washer

Washer

Washer

Washer

Washer

Mechanical

Washer

Washer

Seal MethodWasher

Washer

Washer

Thread

Washer

Thread

BSPTr

threads may vary according to

local and municipal regulations.

Male NPT with Female NPT

Male NPT with Female NPTF

Male NPT with Female NPSM

American Standard Taper

NPT Pipe Thread (National Pipe

Thread

Male NPT with Female NPSH

Female NPT with Male NPT

Female NPT with Male NPTF

Female NPT not compatible with

Male NPSM or Male NPSH

Male NPTF with Female NPTF

Male NPTF with Female NPT

Male NPTF with Female NPSM

Male NPTF with Female NPSH

American Standard Taper

NPTF

Pipe Fuel Dryseal Thread

(National Pipe Tapered

Fine)

Female NPTF with Male NPTF

Female NPTF with Male NPT

Female NPTF with Male NPSM or

Male NPSH

Note: NPTF with NPTF threads

do not require sealant for the

initial use. After that, sealant is

required.

Male NPSH with Female NPSH

American Standard Straight

Female NPSH with Male NPSH

Pipe for Hose Couplings

Female NPSH with Male NPT

(National Pipe Straight

Female NPSH with Male NPTF

Hose)

Female NPSH with Male NPSM

Male NPSM with Female NPSM

American Standard Straight

Male NPSM with Female NPSH

NPSM

Mechanical Joints

(National Pipe Straight

Mechanical)

Female NPSM with Male NPSM

Female NPSM with Male NPT

Female NPSM with Male NPTF

TIPT Tapered Iron Pipe Thread

Generic name for Tapered Pipe

Thread

Washer

Washer

Washer

Washer

Washer

Seal can be

either

mechanical or

washer.

Mating fittings

must be of

same type

Thread

Thread

Thread

Washer

Washer

Thread

Thread

Thread

Thread

Washer

Washer

Thread

Thread

Not

CompatibleNPSH

Thread Dimensions

Nominal Dimensions of Standard Threads

Size

Pipe

NPTNPSH NPSM

IDF

(Min)TPIODMIDF

O. D.

TPITPIODM(Max)(Max)(Min)

270.3970.358

1/8"

.405 27

- - -

180.5260.468

1/4"

.504 18

- - -

180.6620.603

3/8"

.675 18

- - -

1/2"

.840 14 140.82480.7395140.8230.747

3/4"

1.050 14 141.03530.9500141.0340.958

1"

1.315 11.511.51.29511.192111.51.2931.201

1-¼"

1.660 11.511.51.63991.536911.51.6381.546

1-½"

1.900 11.511.51.87881.775811.51.8771.785

2"

2.375 11.511.52.35282.249811.52.3512.259

2.8412.708

3.4673.334

4.4664.333

5.5285.395

6.5856.452

2-½"

2.875 8

- - -

83"

4"

5"

6"

8"

3.500 8

- - -

84.500 8

- - -

85.563 8

- - -

86.625 8

- - -

88.625 8

- - - - - -

10"

10.750 8

- - - - - -

12"

12.750 8

- - - - - -

ODM = Outside Diameter of Male

IDF = Inside Diameter of Female

TPI = Threads per Inch

GHT (¾") = 1.0625 ODM, 11-½ TPI

Pipe

O. D.

TPI

1/8"

.405

1/4"

.504

3/8"

.675

NH (NST)

ODMIDF

BSPP (Parallel)TPIODMIDFBSPTr

(Tapered)

TPI

28

19

19

Size

(Max)(Min)(Max)(Min)0.3830.3370.5160.4500.6560.588- - - -- - - -- - - -

1/2"

.840

- - - --0.8250.7331.0410.95014

14

11

11

11

11

11

11

11

3/4"

1.050 8 1.3751.22461"1.315 8 1.3751.2246111.3091.1931.6501.5341-¼"

1.660

- - - -1-½"

1.900 9 1.9901.8577111.8821.7662"2.375

- - - -2.3472.2312-½"

2.875 7.5 3.0682.9104112.9602.8443"4"3.500 6 3.6233.5306113.4603.3444.500 4 5.0104.7111114.4504.334-4-½" -

4 5.7605.46115"6"- - -

11

11

5.563 4 6.2605.9602115.4505.3596.625 4 7.0256.7252116.4506.359ODM = Outside Diameter of Male

IDF = Inside Diameter of Female

TPI = Threads per Inch

GHT (¾") = 1.0625 ODM, 11-½ TPI

NOTE: Female NPT (Tapered Pipe) thread is not available on

hose swivel nuts.

Normal Engagement Length

of NPT Thread in Inches ("A") *

Size 1/8" 1/4" 3/8"1/2"3/4"1" 1-¼"1-½"2"

Length

1/4" 3/8" 3/8"1/2"9/16"11/16"11/16"11/16"3/4"

Size 2-½" 3" 4" 5" 6" 8" 10" 12"

Length15/16" 1" 1-1/8"1-1/4"1-5/16"1-7/16"1-5/8"1-3/4"

* Dimensions given do not allow for variations in tapping or threading

Thread Sealing Tips

Thread Seal Type

• A seal is obtained by applying a

sealant to the male thread before

engaging.

• The sealant is used to prevent spiral

leakage.

• Thread tape or paste is the preferred

sealant in this type of application.

Washer Seal Type

• A seal is obtained when the male

thread is tightened down onto the

washer of the female assembly.

• The washer should be inspected

regularly and replaced as needed to

prevent leakage.

Mechanical Seal Type

• A seal is obtained through metal to

metal contact or metal to seal

contact, for example JIC couplings

have a metal to metal seal. EZ-Boss

Ground Joint couplings have a metal

to seal contact (shown at left).

• The couplings should be retightened

as needed to prevent leakage.

More Thread

Sealing NPT threads can be an exasperating experience if certain techniques

are not followed. The following tips will help alleviate many common problems

in thread sealing:

• 1. Always use some type of

sealant (tape or paste) and

apply sealant to male thread

only. If using a hydraulic sealant,

allow sufficient curing time

before system is pressurized.

• 2. When using tape sealant,

wrap the threads in a clockwise

motion starting at the first thread

and, as layers are applied, work

towards the imperfect

(vanishing) thread. If the system

that the connection being made

to cannot tolerate foreign matter

(i.e. air systems), leave the first

thread exposed and apply the

tape sealant as outlined above.

• 3. When using paste sealant,

•

•

•

• 6. For sizes 2" and below, tape

or paste usually performs

satisfactorily. When using thread

tape, four wraps (covering all

necessary threads) is usually

sufficient.

7. For sizes 2-½" and above,

thread paste is recommended. If

thread tape is used, eight wraps

(covering all necessary threads)

is usually sufficient. Apply more

wraps if necessary.

8. For stubborn to seal threads,

apply a normal coating of thread

paste followed by a normal layer

of thread tape.

9. For extremely stubborn to

seal threads, apply a normal

apply to threads with a brush,

using the brush to work the

sealant into the threads. Apply

enough sealant to fill in all the

threads all the way around.

• 4. When connecting one

stainless steel part to another

stainless steel part that will

require future disassembly, use

a thread sealant that is designed

for stainless steel. This stainless

steel thread sealant is also

useful when connecting

aluminum to aluminum that

needs to be disconnected in the

future. These two materials gall

easily, and if the correct sealant

is not used, it can be next to

impossible to disassemble.

• 5. When connecting parts made

of dissimilar metals (i.e. steel &

aluminum), standard tape or

paste sealant usually performs

satisfactorily.

•

coating of thread paste followed

by a single layer of gauze

bandage followed by a normal

layer of thread tape.

Caution!

When this procedure is done,

the connection becomes

permanent. Extreme measures

will be necessary to disconnect

these components. All other

measures to seal the threads

should be explored prior to the

use of this technique.

10. Over-tightening threads can

be just as detrimental as

insufficient tightening. For sizes

2" and below, hand tighten the

components and, with a wrench,

tighten 3 full turns. for sizes 2-½"

and above, hand tighten the

components and, with a wrench,

tighten 2 full turns.

2 Pipe Thread Standards

Two common pipe thread standards exist:

•

•

National Pipe Thread (NPT) - a tapered thread

National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM) - a

straight thread

Less common standards also exist:

•

•

•

Garden Hose Thread (GHT)

Fire Hose Coupling (NST)

British Standard Taper Pipe Thread (BSPT)

Female NPT threads can be designated as "FPT" and male NPT threads can be designated

as "MPT." I have also seen female NPT threads designated as "FNPT" and male as "MNPT".

Straight Versus Tapered Threads

Threaded pipe can be connected to join things together, which does not necessarily

produce a leakproof seal, or they can be joined and sealed.

Straight threads only provide a mechanical junction. They don't really seal.

Tapered threads both join and seal. The deeper you drive them, the tighter the seal.

Pipe Thread Tape

Whenever you want a good seal when screwing together pipes and fittings, use pipe thread

tape. This is usually made of PTFE, the most famous brand of which is Teflon.

In addition to sealing, pipe thread tape also lubricates the joint, which:

•

•

•

makes it easier to tighten it

makes it easier to disassemble the joint in the future

reduces/eliminates thread galling [Thread galling is when threads weld

themselves together. This is more common with pipes and fasteners made from

alloys that protect themselves from corrosion by developing their own oxide

surface film, like aluminum and stainless steel.

Standard Pipe Sizes

Pipe sizes do not refer to any physical dimension of modern pipe. If you measure a piece

of 1/4" NPT pipe, you will have a hard time finding anything there that measures 1/4".

Historical note:

• The sizes derive from the days when pipes were made of iron, pipe walls were

rather thick, and the internal diameter (ID) was standardized. At that time,

if you specified a 1/2" pipe, it had an internal diameter of 1/2", and an outer

diameter that depended on the thickness of the wall.

• Nowadays, the standards measure the threaded part of the pipe, the outer diameter

(OD). This lets thin-wall and thick-wall pipe use the same fittings.

• But we kept the same names, so when you say 1/2" pipe, you get a pipe whose outer

diameter is the same as that of an old-fashioned iron pipe whose inner diameter

was 1/2".

In order to get the right size, you should measure the outer diameter (OD) of the pipe,

and look it up in a table to find out what it is officially called. It's also a good

idea to measure the threads per inch (TPI). The combination of OD and TPI provide positive

identification of standard pipe sizes.

OD Fraction OD DecimalNormal depth

(approximate)(actual) for tight joint

5/16"

13/32"

35/64"

43/64"

27/32"

1-3/64

1-5/16"

1-21/32"

1-29/32"

2-3/8"

2-7/8"

3-1/2"

4"

4-1/2"

0.3125"

0.405"

0.540"

0.675"

0.840"

1.050"

1.315"

1.660"

1.900"

2.375"

2.875"

3.5"

4.0"

4.5"

0.2611"

0.2639"

0.4018"

0.4078"

0.5337"

0.5457"

0.6828"

0.7068"

0.7235"

0.7565"

1.1375"

1.2000"

1.2500"

1.3000"

Pipe Thread Size Threads per Inch

1/16"

1/8"

1/4"

3/8"

1/2"

3/4"

1"

1-1/4"

1-1/2"

2"

2-1/2"

3"

3-1/2"

4"

3,

27

27

18

18

14

14

11-1/2

11-1/2

11-1/2

11-1/2

8

8

8

8