Connect 1-1/2" NH fire hose thread (NST) to 1/2" NPT (National Pipe Taper)

A 1-1/2 inch NH fire hose coupling reaches a 1/2 inch NPT pipe through an NH-to-NPT reducing adapter. The NH end seals on its gasket swivel; the NPT end seals on the tapered pipe thread with tape.

NH and NPT are entirely different threads. Do not try to thread a fire coupling onto a pipe port; the pitch and form are unrelated. Use the dedicated adapter.