Aluminum 4" Female NH to 3" Male NH

Item Number: 37R43
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$166.32
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Ships: Approx. Aug 27, 2026
Estimated transit time: 2 to 5 Business Days

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  • The female side of a NH / NST coupling will only connect to a male NH / NST connection
  • The male side of a NH / NST coupling will only connect to a female NH / NST connection
  • The female side of a NPSH coupling will only connect to a male NPT pipe or a male NPSH connection
  • The male side of a NPSH coupling will only connect to a female NPSH connection. It will NOT thread into a female NPT pipe. For example, a male NPSH coupling will NOT thread into a female metal or pvc pipe.
  • The female side of a garden hose will only connect to a male garden hose connection.
  • The male side of a garden hose will only connect to a female garden hose connection.

NH / NST: The most common thread type in use by fire departments today is NST or National Standard Thread. NST also goes by the initials NH or National Hose. It can even be referred to as NHT or National Hose Thread but NST or NH is more common these days. NH = NST.

NPSH: National Pipe Straight Hose (NPSH) or Iron Pipe Thread (IPT) has the same threads per inch (TPI) as National Pipe Tapered (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.

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.

Warranty Information

Limited Lifetime Warranty - We will replace any adapters with manufacturer defects in material and workmanship. All warranty claims must be returned to us for inspection before we determine a solution.

Our warranty does not cover gaskets, multiple use of NPT threads, shipping cost, cosmetic damages, normal wear-and-tear, improper use or chemical damage.

Adapters purchased for use at Fire Training Facilities will have a 90-day Manufacturer Defect warranty only.

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Additional Details

Aluminum adapters are fabricated from seamless extruded 6061-T6 aluminum and hard coat anodized per MIL-A-8625 Type III, Class 1. Threads have a blunt start Higbee cut with indicators on adjacent lugs. Part identifications are permanent and stamped prior to hardcoat. Adapters and components meet the requirements of NFPA 1963.

Note - 3 inch NH / NST is very rare and is often confused with 2.5 inch NH / NST which is very common. If you have a fire department connection (FDC), hose coupling or an adapter check the female coupling for stamped numbers and letters. Most 3.0 inch hoses use 2.5 inch NH / NST couplings. The most common fire fitting thread in the United States is 2 1/2 inch NH /NST.

If you have two swivel female FDC brass connections that need plugs measure the INSIDE diameter of the swivel fitting. If it measures approximately 3 inches, you need 2 1/2 inch NH / NST plugs. 3 inch NH / NST fittings measure approximately 3 5/8". If you have any doubt it is best to contact your local fire department for size and thread type in your area.

If possible it is best to measure the MALE fitting. The outside diameter of a 2.5 inch NH / NST male hose coupling or fire hydrant is 3.06 inches. The outside diameter of a 3.0 inch NH / NST male hose coupling or fire hydrant is 3.62 inches. The outside diameter of a 2.5 inch NPT or NPSH male hose coupling is 2.84 inches. The outside diameter of a 3.0 inch NPT or NPSH male hose coupling is 3.47 inches.

The Safe Water Drinking Act section 1417 requires "Lead-Free" products to be a minimum of 99.75% lead-free.

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Specifications

  • Made in USA
  • O.D. of a 3 inch Male NH / NST is 3 5/8 inch and Rare
  • READ FULL DESCRIPTION BELOW
  • Female Side: 4 inch NH / NST
  • The Female Will Only Connect to a Male 4 inch NH / NST
  • Male Side: 3 inch NH / NST
  • The Male Will Only Connect to a Female 3 inch NH / NST
  • Material: 6061-T6 Aluminum
  • Finish: Hard Coat Anodized
  • Complies With NFPA 1963 (Corrosion Resistance)
  • 99.95% Lead-Free
Garden Hose Thread Male Adapter
  • Outside diameter of a male GHT adapter: 1 1/16 inches (1.06) - 11.5 Threads per inch
1" Male Adapter
  • Inside diameter of a male adapter: 1 inch
  • Outside diameter of a male NH / NST adapter: 1 3/8 inches (1.375) - 8 Threads per inch
  • Outside diameter a male NPSH or NPT adapter: 1 5/16 inches (1.295) - 11.5 Threads per inch
1 1/2" Male Adapter
  • Inside diameter of a male adapter: 1 1/2 inches
  • Outside diameter of a male NH / NST adapter: 2 inches (1.99) - 9 Threads per inch
  • Outside diameter a male NPSH or NPT adapter: 1 7/8 inches (1.87) - 11.5 Threads per inch
1 3/4" Hose Couplings
  • 1 3/4 inch hoses come with 1 1/2 inch couplings
2" Male Adapter
  • Inside diameter of a male adapter: 2 inch
  • Outside diameter of a male NH / NST adapter: 2 1/2 inches (2.51) - 8 Threads per inch
  • Outside diameter a male NPSH or NPT adapter: 2 3/8 inches (2.35) - 11.5 Threads per inch

Note - 2 inch NH or NST is very rare. If the outside diameter of male adapter is approximately two inches, you need 1 1/2 inch NH or NST.

2 1/2" Male Adapter
  • Inside diameter of a male adapter: 2 1/2 inches
  • Outside diameter of a male NH / NST adapter: 3 1/16 inches (3.06) - 7.5 Threads per inch
  • Outside diameter a male NPSH or NPT adapter: 2 7/8 inches (2.84) - 8 Threads per inch
3" Hose Couplings
  • Most 3 inch hoses come with 2 1/2 inch couplings
4" Male Adapter
  • Inside diameter of a male adapter: 4 inches
  • Outside diameter of a male NH / NST adapter: 5 inches (5.01) - 4 Threads per inch
  • Outside diameter a male NPSH or NPT adapter: 4 1/2 inches (4.47) - 8 Threads per inch
5" Male Adapter
  • Inside diameter of a male adapter: 5 inches
  • Outside diameter of a male NH / NST adapter: 6 1/4 inches (6.26) - 4 Threads per inch
6" Male Adapter
  • Inside diameter of a male adapter: 6 inches
  • Outside diameter of a male NH / NST adapter: 7 1/32 inches (7.025) - 4 Threads per inch

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