Not a direct fit. Joining 3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper) needs a 3 NH to 3 NPT fire hose adapter. Sealing method, the real-world trap, and the exact adapter to buy.

Updated 05 September 2026.

HoseFitFinder / Every thread and fitting standard

Connect 3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper)

How to join 3-6NH and 3-8 NPT, and what stops it leaking.

Needs adapter
End A
3" NH fire hose thread (NST) (3-6NH)
Seals on rubber gasket in the female swivel
via adapter
End B
3" NPT (National Pipe Taper) (3-8 NPT)
Seals on on the thread flanks with PTFE tape
Adapter needed3 NH to 3 NPT fire hose adapter

Not a direct fit. Joining 3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper) needs a 3 NH to 3 NPT fire hose adapter.

The adapter to buy

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A 3 NH (National Hose / NST) fire coupling seals on a gasket in its swivel, while 3 NPT seals on a tapered pipe thread, so the two do not interchange even at the same nominal size. An NH-to-NPT adapter carries the gasket-sealed hose thread on one face and the tapered pipe thread on the other.

NH and NPT are unrelated thread forms. Do not try to thread a fire coupling onto a 3 pipe port; use the dedicated NH-to-NPT adapter.

Related connections

3" NH fire hose thread (NST)3-6NH3" NPT (National Pipe Taper)3-8 NPT3" NPT (National Pipe Taper) to 3" BSP parallel (G3 / BSPP)adapter3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT)adapter3" NPSH straight hose thread to 3" NPT (National Pipe Taper)adapter3" BSP parallel (G3 / BSPP) to 3" NH fire hose thread (NST)adapter

Questions and answers

Connect 3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper)?

Not a direct fit. Joining 3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper) needs a 3 NH to 3 NPT fire hose adapter.