Not a direct fit. Joining 1-1/2" NH fire hose thread (NST) to 1-1/2" NPT (National Pipe Taper) needs a 1-1/2 NH to 1-1/2 NPT fire hose adapter. Sealing method, the real-world trap, and the exact adapter to buy.
Updated 05 September 2026.
Connect 1-1/2" NH fire hose thread (NST) to 1-1/2" NPT (National Pipe Taper)
How to join 1-1/2-9NH and 1-1/2-11.5 NPT, and what stops it leaking.
Not a direct fit. Joining 1-1/2" NH fire hose thread (NST) to 1-1/2" NPT (National Pipe Taper) needs a 1-1/2 NH to 1-1/2 NPT fire hose adapter.
The adapter to buy
A 1-1/2 NH (National Hose / NST) fire coupling seals on a gasket in its swivel, while 1-1/2 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 1-1/2 pipe port; use the dedicated NH-to-NPT adapter.
Related connections
Questions and answers
Connect 1-1/2" NH fire hose thread (NST) to 1-1/2" NPT (National Pipe Taper)?
Not a direct fit. Joining 1-1/2" NH fire hose thread (NST) to 1-1/2" NPT (National Pipe Taper) needs a 1-1/2 NH to 1-1/2 NPT fire hose adapter.