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Thread Standards

Thread Standards

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When attaching two threaded devices together, there are a number of factors that come into play. The critical ones are size, thread standard and gender. Material composition is also a factor -- aluminum, brass, copper, plastic, iron, galvanized, etc. In fire fighting, coupling devices are mainly aluminum or brass. Plastic is not common but can be used selectively. Galvanized and iron should be avoided due to the rusting factor. Typically, copper is not used in firefighting systems.

When talking threads, you will encounter numerous types or systems. Generally speaking, NPSH is used in Canada for the smaller hoses (1" & 1½") with NST (NH) used in USA. Forestry applications typically use NPSH or quarter turn quick connect fittings.The charts below will outline characteristics of various thread standards.

Abbreviation System Name Seal Method Thread Compatibility Examples
NPT American Standard Taper Pipe Thread (National Pipe Tapered) Thread Seal or
Washer Seal*
Male NPT - Female NPT, NPTF, NPSM*, NPSH *
Female NPT - Male NPT, NPTF
NPSH American Standard Straight Pipe for Hose Couplings (National Pipe Straight Hose) Washer Seal Male NPSH - Female NPSH, NPSM
Female NPSH - Male NPSH, NPT, NPTF, NPSM
NH or NST American Standard Fire Hose Coupling Thread (National Hose Thread also known as National Standard Thread) Washer Seal Male NH (NST)- Female NH(NST)
Female NH (NST)- Male NH (NST)
Not compatible with other systems. Thread pitch and diameters of fire threads may vary according to local and municipal regulations.
GHT Garden Hose Thread Washer Seal Male GHT - Female GHT
Female GHT - Male GHT
Not compatable with other systems.
NPTF American Standard Taper Pipe Fuel Dry Seal Thread (National Pipe Tapered) Thread Seal or
Washer Seal*
Male NPTF - Female NPTF, NPT, NPSM*, NPSH*
Female NPTF - Male NPTF, NPT
IPS Iron Pipe Straight Thread Washer Seal Generic Name for Straight Pipe Thread (NPSH)
IPT Iron Pipe Thread   Generic Name for All Pipe Thread
More information is needed.
TIPT Tapered Iron Pipe Thread Thread Seal Generic Name for Tapered Pipe Thread (NPT)
CHT Chemical Hose Thread
(also known as Booster Hose Thread). Same as 1" National Hose Thread (NH) or American Standard Fire Hose Thread (NST)
Washer
Seal
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
BSPP British Standard Pipe Parallel Washer Seal Male BSPP - Female BSPP
Female BSPP - Male BSPP
Female BSPP - Male BSPTr
M-BSPP not compatible /w F-BSPTr
BSPTr British Standard Pipe Tapered Thread Seal or
Washer Seal*
Male BSPTr - Female BSPTr, BSPP*
Female BSPTr - Male BSPTr
F-BSPTr not compatible /w M-BSPP

Numerous other thread standards may be encountered. In USA, larger cities or specific municipalities may use unique standards for municipal water and fire fighting services. Examples are New York City Fire Department Thread and Chicago Fire Deptartment Thread. One reason for these unique threads may be to reduce occurrences of theft of hoses and accessories.

Canada also has unique threads -- often by province. You may encounter CSA, BCT, QST, NFLD, NSST, WCT, etc. If you need to be compatible with your local fire department, you should determine what they use and what you would need to attach to their equipment.



COMMONLY USED THREADS
  National
Standard
Thread
NH/NST
Straight
Iron Pipe

NPSH/IPT
Standard
Pipe
Thread
NPT/TIPT
British
Standard
Pipe Thread
BSP
Size ODM TPI ODM TPI ODM TPI ODM TPI
¾" 1.375 8 1.035 14 1.050 14    
1" 1.375 8 1.295 11.5 1.315 11.5 1.309 11
1½" 1.990 9 1.878 11.5 1.900 11.5    
2" 2.515 8 2.352 11.5 2.375 11.5 1.882 11
2½" 3.068 7.5 2.841 8 2.875 8    
3" 3.623 6 3.470 8 3.500 8 2.960 11
3½" 4.243 6 3.970 8 4.000 8 4.125 3
4" 5.010 4 4.470 8 4.500 8 4.625 3
4½" 5.760 4 4.970 8 5.000 8 5.125 3
5" 6.260 4     5.563 8 5.625 3
6" 7.025 4     6.625 8 6.625 3
            Note:
                    Residential garden hose fittings are ¾" GHT with 1.0625" ODM x 11½ TPI


STANDARD FIRE DEPARTMENT 2½" HOSE THREADS
SIZE DESCRIPTION ODM TPI
2½" AMA - Alberta Mutual Aid 2.990 8
2½" BCT - British Columbia 3.000 8
2½" CSA - Canadian Standards Association - Ontario 3.125 5
2½" QST - Province of Quebec Standard 3.031 7
2½" Western Canada Fire Underwriters Association 3.250 6
2½" Nova Scotia - Zone 1 3.230 5V*
2½" Newfoundland -- (aka St. John's thread) 3.25 5V*
2½" NST - American Standard Fire Hose -- USA 3.068 7.5
* It should be noted that most fire hose threads are blunt at the top -- but the 5V thread is cut to a sharp "V" point. To do this, the depth of the thread is 1/64th of an inch deeper than the conventional 5 threads-to-the-inch of the Canadian Standard Fire HoseThread.


OTHER COMMON FIRE HOSE THREADS - mainly USA
SIZE DESCRIPTION ODM TPI
¾" STD Chemical Thread 1.375 8
1½" Underwriter TIP 2.187 12
2½" *Chicago Fire Dept. Thread 2.990 7.5
2½" Cincinnati, OH 3.058 6
2½" Clevland, OH ... also Omaha, NE 3.078 8
2½" Pittsburgh, PA 3.062 6
2½" Detroit, MI 3.125 7.5
2½" Denver, CO 3.092 8
2½" New York Fire Dept. Thread 3.030 8
2½" Pacific Coast Thread 3.035 7.5
2½" Salt Lake City, UT 3.250 6
2½" Toledo, OH 3.000 8
* It should be noted that there is a Chicago Fire Dept Thread standard as well as a Chicago Hose Thread standard — covering various sizes of hose. They contain different specifications.



One Stop Fire Products Inc.
Markham, Ontario
L3P 7H9
Canada
Tel: (905) 946-1033
Fax: (905) 946-1035
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