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Thread Data
Intro Pic

Identifying Threads

It is important to identify the threads required before ordering the couplings!
Identifying threads can sometimes be the most difficult and frustrating part of coupling selection. However, without the right combination of threads, you may not provide a functional or safe connection.
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

Straight Thread - Male   Straight Thread - Female
Male   Female

Tapered Thread

Tapaerd Thread - Male   Tapered Thread - Female
Male   Female

Threading Information

AbbreviationSystem NameCompatibilitySeal Method
BSPPBritish Standard Pipe ParallelMale BSPP with Female BSPPWasher
Female BSPP with Male BSPPWasher
Female BSPP with Male BSPTrWasher
BSPTrBritish Standard Pipe TaperMale BSPTr with Female BSPTrThread
Male BSPTr with Female BSPPWasher
Female BSPTr with Male BSPTrThread
Female BSPTr not compatible
with Male BSPP
CHTAmerican Standard Fire Hose Thread (1" National Hose Thread is Chemical Hose Thread, also known as Booster Hose Thread)1"Male NH (NST) with 1" Female NH (NST)Washer
1" Female NH (NST) with 1" Male NH (NST)Washer
1" Thread is used on both ¾" hose & 1" hose. 
Not compatible with other systems 
GHTGarden Hose ThreadMale GHT with Female GHTWasher
Female GHT with Male GHTWasher
Thread is the same for all size hose. 
Not compatible with other systems 
IPSIron Pipe Straight ThreadGeneric name for Straight Pipe ThreadWasher
See NPSH for compatibility 
JICJoint Industrial CommitteeUsed with other mating JIC threadsMechanical
American Standard Fire Hose Coupling Thread (National Hose thread also known as National Standard ThreadMale NH (NST) with Female NH (NST)Washer
Female NH (NST) with Male NH (NST)Washer
Not compatible with other systems
Thread pitch and diameters of fire threads may vary according to local and municipal regulations.
NPTAmerican Standard Taper Pipe Thread (National Pipe ThreadMale NPT with Female NPTThread
Male NPT with Female NPTFThread
Male NPT with Female NPSMWasher
Male NPT with Female NPSHWasher
Female NPT with Male NPTThread
Female NPT with Male NPTFThread
Female NPT not compatible with Male NPSM or Male NPSH 
NPTFAmerican Standard Taper Pipe Fuel Dryseal Thread (National Pipe Tapered Fine)Male NPTF with Female NPTFThread
Male NPTF with Female NPTThread
Male NPTF with Female NPSMWasher
Male NPTF with Female NPSHWasher
Female NPTF with Male NPTFThread
Female NPTF with Male NPTThread
Female NPTF with Male NPSM or Male NPSHNot Compatible
Note: NPTF with NPTF threads do not require sealant for the initial use. After that, sealant is required. 
NPSHAmerican Standard Straight Pipe for Hose Couplings (National Pipe Straight Hose)Male NPSH with Female NPSHWasher
Female NPSH with Male NPSHWasher
Female NPSH with Male NPTWasher
Female NPSH with Male NPTFWasher
Female NPSH with Male NPSMWasher
NPSMAmerican Standard Straight Mechanical Joints (National Pipe Straight Mechanical)Male NPSM with Female NPSMSeal can be either mechanical or washer. Mating fittings must be of same type
Male NPSM with Female NPSH
Female NPSM with Male NPSM
Female NPSM with Male NPT
Female NPSM with Male NPTF
TIPTTapered Iron Pipe ThreadGeneric name for Tapered Pipe ThreadThread

Thread Dimensions
Nominal Dimensions of Standard Threads

O. D.
ODM = Outside Diameter of Male
IDF = Inside Diameter of Female
TPI = Threads per Inch
GHT (¾") = 1.0625 ODM, 11-½ TPI

O. D.
NH (NST)BSPP (Parallel)BSPTr
ODM = 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") *

Thread Engagement


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

Thread Sealing Tips

Thread Sealing -
Thread Seal TypeThread 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.
Thread Sealing -
Washer Seal TypeWasher 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.
Thread Sealing -
Mechanical Seal TypeMechanical 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 Tips...

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, 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.
  • 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 coating of thread paste followed by a single layer of gauze bandage followed by a normal layer of thread tape.
    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.





Tampa Rubber & Gasket Co., Inc.

215 North 20th Street
Tampa, FL, USA 33605
Ph-813-247-3647 Fax-813-247-3180
Toll Free-800-940-4673 E-Mail - The Post Office
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