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. Ring, Plug and GO/NOGO 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. Dixon offers 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:
Once the application and these two pieces of information have been determined, the thread can generally be determined. When in doubt, contact the factory.
Male BSPP with Female BSPPFemale BSPP with Male BSPPFemale BSPP with Male BSPTr
WasherWasherWasher
Male BSPTr with Female BSPTrMale BSPTr with Female BSPPFemale BSPTr with Male BSPTrFemale BSPTr not compatible with MaleBSPP
ThreadWasherThread
American Standard Fire Hose Thread(1" National Hose Thread is ChemicalHose Thread, also known as BoosterHose Thread)
1" Male NH (NST) with 1" Female NH (NST)1"Female NH (NST) with 1" Male NH (NST)1" Thread is used on both ¾" hose and 1"hose.Not compatible with other systems
WasherWasher
Male GHT with Female GHTFemale GHT with Male GHTThread is same for all size hoseNot compatible with other systems
Generic Name for Straight Pipe ThreadSee NPSH for compatibility
Washer
Generic Name for All Pipe ThreadMore information required
American Standard Fire Hose CouplingThread(National Hose thread also known asNational Standard Thread)
Male NH (NST) with Female NH (NST)Female NH (NST) with Male NH (NST)Not compatible with other systemsThread pitch and diameters of fire threadsmay vary according to local and municipalregulations
American Standard Taper Pipe Thread(National Pipe Tapered)
Male NPT with Female NPTMale NPT with Female NPTFMale NPT with Female NPSMMale NPT with Female NPSHFemale NPT with Male NPTFemale NPT with Male NPTFFemale NPT not compatible with Male NPSMor Male NPSH
ThreadThreadWasherWasherThreadThread
American Standard Taper Pipe FuelDryseal Thread (National Pipe TaperedFine)
Male NPTF with Female NPTFMale NPTF with Female NPTMale NPTF with Female NPSMMale NPTF with Female NPSHFemale NPTF with Male NPTFFemale NPTF with Male NPTFemale NPTF with Male NPSM or NPSHNote: NPTF with NPTF threads do notrequire sealant for the initial use. After that,sealant is required
ThreadThreadWasherWasherThreadThreadNot Compatible
American Standard Straight Pipe forHose Couplings (National Pipe StraightHose)
Male NPSH with Female NPSHFemale NPSH with Male NPSHFemale NPSH with Male NPTFemale NPSH with Male NPTFFemale NPSH with Male NPSM
WasherWasherWasherWasherWasher
American Standard Straight MechanicalJoints (National Pipe StraightMechanical)
Male NPSM with Female NPSMMale NPSM with Female NPSHFemale NPSM with Male NPSMFemale NPSM with Male NPTFemale NPSM with Male NPTF
Seal can be eithermechanical or washer.Mating fittings must beof same type
Nominal dimensions of Standard Threads
1/8"1/4"3/8"
.405.540.675
271818
281919
0.3970.5260.662
0.3580.4680.603
0.3830.5160.656
0.3370.4500.588
1/2"3/4"1"1-1/4" 1-1/2"2"2-1/2"
.8401.0501.3151.6601.9002.3752.875
141411.511.511.511.58
14141111111111
0.82481.03531.29511.63991.87882.35282.8434
0.73950.95001.19211.53691.77582.24982.6930
0.8231.0341.2931.6381.8772.3512.841
0.7470.9581.2011.5461.7852.2592.708
8
9
7.5
1.375
1.990
3.068
1.2246
1.8577
2.9104
1111
0.8251.0411.3091.6501.8822.3472.960
0.7330.9501.1931.5341.7662.2312.844
3"4"4-1/2"5"6"
3.5004.500
5.5636.625
88
3.4674.466
5.5286.585
3.3344.333
5.3956.452
64444
3.6235.0105.7606.2607.025
3.53064.71115.46115.96026.7252
11
3.4604.450
5.4506.450
3.3444.334
5.3596.359
8"10"12"
8.62510.75012.750
888
Dimensions given do not allow for variations in tapping or threading.
1/8"1/4"3/8"1/2"3/4"1"1-1/4"1-1/2"2"2-1/2"3"4"5"6"8"10"12"
1/4"3/8"3/8"1/2"9/16"11/16"11/16"11/16"3/4"15/16"1"1-1/8"1-1/4"1-5/16"1-7/16"1-5/8"1-3/4"
National Standard
NH
StraightIron Pipe
NPSH
New YorkCorporation
NYCT
Pacific Coast
PCT
New YorkFire Dept.
NYFT
Chemical HoseCHT *
Underwriter'sPlay Pipe
PPS
GardenHose
GHT *
Chicago FireDept.
(NEW) *
¾"1"1¼"1½"2"2½"3"3½"4"4½"5"6"
1.3751.3751.67181.9902.51563.06863.62394.24395.01095.76096.2607.025
889987½664444
1.0353 *1.2951 *1.6399 *1.8788 *2.3528 *2.841 *3.4703.9704.4704.9705.5306.590
1411½11½11½11½8888888
------2.0932.5473.000------------
------11118------------
1.06251.31251.8602.1002.5503.035----5.000------
1111½1111107½----4------
--1.660--2.100--3.0303.6304.0704.6105.800----
--8--8--88884----
1.3751.370--------------------
88--------------------
------2.1875----------------
------12----------------
1.06251.0625--------------------
11½11½--------------------
------1.933--2.990------------
------11½--7½------------
1.0811.29511.7051.9462.5223.043------------
11½11½11½11½87------------
* National Form Thread. Abbreviation for tapered iron pipe thread is TIPT or NPT (National Pipe Tapered).
ODM = Outside Diameter of Male
2½"2½"2½"2½"2½"2½"
AMA - Alberta Mutal AidBCT - British Columbia - VancouverCSA - Canadian Standards Association - OntarioQST - Provice of Quebec StandardWestern Canada Fire Underwriters Association - Winnipeg, SaskatoonNova Scotia - Male .010 flat x female, Sharp V
2.99033.1253.0313.2503.230
8 *8 *5 *765
* Truncated
