How it connects
Straight mechanical threads draw the male nose against a rubber/elastomer gasket seated in the mating female swivel nut to create a compression seal.
Male and female halves
Male external parallel thread that mates with a female swivel collar containing an internal sealing gasket.
Usually connects to
- Matching female NPSH swivel hose coupling with gasket, including 1-1/2 in
- Same-size female NPT can engage partially/loosely; sealing descriptions differ between gasket and tape/sealant, so it is not the recommended direct pairing
Common sizes
- NPSH nominal sizes span about 1/2–4 in and larger, commonly 3/4, 1, 1-1/2, 2 and 2-1/2 in.
- Shares NPT pitch by nominal size: e.g. 14 TPI at 3/4 in and 11.5 TPI at 1–2 in. A 1-1/2 in example has about 1.878 in (47.7 mm) thread OD.
Where it is used
firefighting hose linesindustrial washdownwater pump discharge and suctionmill hose assemblies; fire hose and forestry hoseconstruction dewateringindustrial/water hose couplingspump and tank connectionsplumbing appliance inlets
Variations
- Cast brass male shank coupling
- Extruded or cast aluminum pin-lug shank coupling
- Rocker lug coupling
- Hex nipple adapter (NPSH to NPT)
- NPSM (straight mechanical pipe thread, similar)
- NPSH male nipple
- NPSH female swivel
How to recognise it
External parallel cylindrical threads measuring ~1.88" (47.7 mm) in diameter with 11.5 TPI pitch, a flat blunt leading nose to press against a gasket, and often integrated pin lugs or rocker lugs on the hose shank body.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| 1-1/2 inch NH / NST (National Hose / National Standard Thread) | 1-1/2" NH/NST has a larger outside diameter (1.990 inches) and coarser pitch (9 TPI), whereas 1-1/2" NPSH has 11.5 TPI and ~1.878 inches OD. |
| NPT pipe thread | NPT threads are tapered (1:16) and designed to seal on thread interference/tape, whereas NPSH threads are parallel (straight) and require a gasket in the mating female coupling. NPT threads taper and seal in the threads; NPSH stays the same diameter along its length and needs a gasket. |
| NH / NST / GHT hose threads | NH/NST and GHT have coarser, different-diameter threads (e.g. 3/4 GHT is 11.5 TPI on ~1.06 in OD); NPSH matches pipe-thread diameters. |
| NPSM | Close cousin in ASME B1.20.1 used for mechanical joints; dimensions are nearly the same, but NPSH is the hose-coupling form from B1.20.7. |
Also called
1-1/2" NPSH male thread1-1/2" IPT male hose thread1.5 inch NPSH couplingMNPSHAmerican Standard Straight Pipe Thread for hose couplings
Good to know
A male 1-1/2" NPSH thread will mechanically thread into a female 1-1/2" NPT port because they share the same pitch (11.5 TPI) and basic diameter, but female NPSH couplings will not properly seal on a male NPT pipe unless an appropriate seating gasket is used.
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