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Adapter Guide

How To Connect Using NH / NST, NPSH and NPT Threads

Adapter Selection Guide
I want to convert...I need... (Female to Male Adapter)
 Most fire hydrants to fire hose  NH to NH
 Male PVC or metal pipe fitting to fire hose  NPT or NPSH to NH
 Female PVC or metal pipe fitting to fire hose  NPT to NH
 Most fire hydrants to forestry hose  NH to NPSH (check forestry hose thread type)
 Garden hose thread to fire hose  GHT to NH
 Note: NH = NST and NPSH = IPT


Storz Measurement Guide
Storz DescriptionInside Distance Between Lugs
 1 inch or 25mm  1 7/32 inches or 31mm
 1 1/2 inch or 38mm  2 1/16 inches or 52mm
 2 inch or 50mm  2 5/8 inches or 66mm
 2 1/2 inch or 65mm  3 3/16 inches or 81mm
 3 inch or 75mm  3 1/2 inches or 89mm
 4 inch or 100mm  4 1/2 inches or 115mm
 5 inch or 125mm  5 13/16 inches or 148mm

Commonly Used U.S. Fire Hose Connection Threads
MaleNational StandardNational Pipe Straight Hose
 Size NH or NST NPSH or NPT
 IDM  ODM  Circumference  TPI  ODM  Circumference  TPI
 3/4"  1.375  4.32  8  1.035  3.25  14
 1"  1.375  4.32  8  1.295  4.07  11.5
 1 1/2"  1.990  6.25  9  1.878  5.89  11.5
 2"  2.515  7.90  8  2.352  7.39  11.5
 2 1/2"  3.068  9.64  7.5  2.841  8.93  8
 3"  3.623  11.38  6  3.470  10.90  8
 3 1/2"  4.243  13.33  6  3.970  12.47  8
 4"  5.010  15.74  4  4.470  14.04  8
 4 1/2"  5.760  18.09  4  4.970  15.61  8
 5"  6.260  19.67  4      
 6"  7.025  22.07  4      

**Garden Hose Thread (GHT) has 1.0625 ODM and 11.5 TPI

ODM = Outside Diameter of Male

TPI = Threads Per Inch

Abbreviations for tapered iron pipe thread is NPT (National Pipe Tapered) or TIPT (Tapered Iron Pipe Thread) - mechanical seal

Abbrev. for straight iron pipe thread is NPSH (National Pipe Straight Hose), IPT or SIPT (Straight Iron Pipe Thread) - gasket seal

Abbrev. for straight fire hose thread is NH (National Hose) or NST (National Standard Thread) - gasket seal.

For additional information on measuring and identifying threads from Dixon Powhatan and Red Head Brass see links below.

Identifying Threads Specs and Diagrams

Common Questions Answered

Couplings are the aluminum or brass ends connected to hose and threads are the grooves in or on the couplings that make connecting a hose to a water source or to another hose possible. The male coupling has threads on the outside and the female coupling has threads on the inside. Anodized hardcoated aluminum couplings are common for most firefighting, industrial and other uses today. When compared to brass, aluminum is less likely to crossthread as it is a harder metal, is lighter weight and more economical. Brass is still used where corrosion is an issue, especially in a saltwater environment.

How do you determine what thread type you need? The easiest way to determine thread type is to check the couplings on the hose you are seeking to replace for the initials of the thread type. Sometimes the water source fitting or adapter is stamped as well. If you are connecting to a hydrant or other fire equipment a call to the local fire department can help determine thread type. If you are careful and precise you may also count TPI or Threads Per Inch and/or measure the ODM or Outside Diameter of the Male coupling (this is tricky for NPT) to help determine thread type. Please see chart and links above for details.

There are three primary threads in use nationally today as well as a number of regional threads. Though there are some cases where different threads may be compatible for the most part they are not and it is critical that the correct thread is specified. If a mistake is made however, or there is a desire to make an existing hose or outlet compatible with another thread FireHoseDirect does offer a variety of adapters to make that possibe.

NH or NST: National Hose or National Standard Thread is often referred to as “fire hose thread” as this is by far the most common thread in use today by fire departments. This is a “straight” thread which means fitting size is consistent from tip to collar and the seal is made via the gasket inside the female coupling mating against the square face of the male coupling. This is similar to common garden hose connections. The threads do not make the seal, they merely hold the two fittings tightly together.

NPT: National Pipe Tapered is common in plumbing and some industrial uses. Sometimes referred to as “pipe thread” because PVC pipe and schedule 40 pipe are typically threaded in NPT. As its name implies this is a tapered thread so that the outside diameter of the male (ODM) gets smaller towards the end of the fitting and the inside diameter of the female narrows with depth. As the two fittings are threaded together the opposite tapers force thread friction and makes the seal without the use of a gasket. This is why pipe compound or thread tape is often used on NPT threads to insure a good seal. Rate of taper is 1/16, so only 1/16" per 1 inch of thread, 1/32" per 1/2 inch of thread.

NPSH or IPT: National Pipe Straight Hose or Iron Pipe Thread has the same TPI as NPT but the thread does not taper. NPSH is a straight thread and seals by a gasket in the female coupling which allows for a swivel, just like NH/NST, which make both ideal for hose couplings. A male NPSH or a male NPT will thread into a female NPSH. The seal should be good as long as the male fitting is square to make a good seal with the gasket. In the case of PVC pipe into a female NPSH you may still want to consider using an aluminum or brass female NPT to male NPSH adapter if the fitting will be threaded on and off frequently. The metal to metal connection should wear better than the metal to PVC and the slightly larger diameter of the male NPSH should make a better seal with the female NPSH gasket.

Since the male NPSH fitting does not taper it cannot thread far enough into a female NPT fitting to make a good seal; the taper in the female NPT prevents this. In some diameters you may be able to thread a male NPSH a turn or two into a female NPT but you will not have a good seal. Male NPSH into female NPT is not compatible.

Another thread is GHT or Garden Hose Thread. This thread seals via washer in the female coupling and is not compatible with the other threads mentioned above. A typical garden hose may be 5/8" or 3/4" I.D. but the fitting on the ends will be GHT. We have adapters to convert NH or NPSH to GHT and vice versa.

Adapter connectors are available to convert from one thread spec to another as well and increase or reduce diameter. When looking for threaded adapters you may see the letter M or F or sometimes FM in front of the thread type. This stands for Male or Female. For example 2.0" FM NPT x 1.5" M NH threaded adapter will allow you to connect and 1.5 inch NH coupled fire hose to what was a 2.0" male NPT supply outlet.

When shopping for a fire hose nozzle make sure it is compatable with your hose coupling. We offer both NH/NST and NPSH/IPT nozzles at FireHoseDirect.  Please see our nozzle section for both economy nozzles and full fledged fire department grade everyday firefighting nozzles.

Higbee: This is the short flat triangular fade at the tip of a male NST/NH thread, as opposed to a thin thread beginning on NPT, that allows attaching a fire hose coupling quickly to another coupling or to the water supply outlet without jamming via cross-threading. There is typically a notch on one of the male and female coupling rocker lugs to locate the "Higbee", called a "Higbee Cut". Line these notches up to make joining two lengths of hose quick and easy. NFPA 1963 requires a Higbee on NH thread.

Thread Compatibility
 System NameCompatibilitySeal Method
 BSPP  British Standard Pipe Parallel  Male BSPP with Female BSPP
 Female BSPP with Male BSPP
 Female BSPP with Male BSPTr
 BSPTr  British Standard Pipe Taper  Male BSPTr with Female BSPTr
 Male BSPTr with Female BSPP
 Female BSPTr with Male BSPTr
 Female BSPTr not compatible with Male BSPP
 CHT  American 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)
 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
 GHT  Garden Hose Thread  Male GHT with Female GHT
 Female GHT with Male GHT
 Thread is same for all size hose
 Not compatible with other systems
 IPS  Iron Pipe Straight Thread  Generic Name for Straight Pipe Thread
 See NPSH for compatibility
 IPT  Iron Pipe Thread  Generic Name for All Pipe Thread
 More information required
 NH / NST  American Standard Fire Hose Coupling Thread (National Hose thread also known as National Standard Thread)  Male NH (NST) with Female NH (NST)
 Female NH (NST) with Male NH (NST)
 Not compatible with other systems
 Thread pitch and diameters of fire threads may vary according to local and municipal regulations.
 NPT  American Standard Taper Pipe Thread
 (National Pipe Tapered)

 Male NPT with Female NPT
 Male NPT with Female NPTF
 Male NPT with Female NPSM
 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

 NPTF  American Standard Taper Pipe Fuel Dryseal Thread (National Pipe Tapered Fine)  Male NPTF with Female NPTF
 Male NPTF with Female NPT
 Male NPTF with Female NPSM
 Male NPTF with Female NPSH
 Female NPTF with Male NPTF
 Female NPTF with Male NPT
 Female NPTF with Male NPSM or NPSH
 Note: NPTF with NPTF threads do not require sealant for the initial use. After that, sealant is required.
 Not Compatible
 NPSH  American Standard Straight Pipe for Hose Couplings (National Pipe Straight Hose)  Male NPSH with Female NPSH
 Female NPSH with Male NPSH
 Female NPSH with Male NPT
 Female NPSH with Male NPTF
 Female NPSH with Male NPSM
 NPSM  American Standard Straight Mechanical Joints (National Pipe Straight Mechanical)  Male NPSM with Female NPSM
 Male NPSM with Female NPSH
 Female NPSM with Male NPSM
 Female NPSM with Male NPT
 Female NPSM with Male NPTF
 Seal can be either mechanical or washer. Mating fittings must be of same type.
 SIPT  Straight Iron Pipe Thread  Generic name for Straight Pipe Thread  Washer
 TIPT  Tapered Iron Pipe Thread  Generic name for Tapered Pipe Thread  Thread