Connect 2-1/2" NH fire hose thread (NST) to 1-1/2" NH fire hose thread (NST)
How to join 2-1/2-7.5NH and 1-1/2-9NH, and what stops it leaking.
Needs adapter
End A
2-1/2" NH fire hose thread (NST) (2-1/2-7.5NH)
Seals on rubber gasket in the female swivel
via adapter
End B
1-1/2" NH fire hose thread (NST) (1-1/2-9NH)
Seals on rubber gasket in the female swivel
Adapter needed2-1/2 NH to 1-1/2 NH fire hose reducer
Not a direct fit. Joining 2-1/2" NH fire hose thread (NST) to 1-1/2" NH fire hose thread (NST) needs a 2-1/2 NH to 1-1/2 NH fire hose reducer.
The adapter to buy
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Reducing a 2-1/2 inch NH line to 1-1/2 inch NH uses a fire hose reducer. Both are NH gasket-sealed threads at different pitches, so the reducer carries the correct thread on each face.
Even within NH the pitch changes with size: 7.5 TPI at 2-1/2 inch, 9 TPI at 1-1/2 inch. A same-thread assumption fails; use the sized reducer.
Related connections
2-1/2" NH fire hose thread (NST)2-1/2-7.5NH1-1/2" NH fire hose thread (NST)1-1/2-9NH1-1/2" NH fire hose thread (NST) to 1/2" NPT (National Pipe Taper)adapter2-1/2" NH fire hose thread (NST) to 1" NPT (National Pipe Taper)adapter
Sources: NFPA 1963 (fire hose connections, NH / NST) · NPSH / NH / NHR hose coupling thread table, Fittings.space