MARINE thru-hulls, tailpipes, valves and seacocks have parallel threads known as “American Standard Straight Mechanical” pipe threads or “NPSM”. These require thread compound or Teflon tape to seal.
INDUSTRIAL or household fittings are tapered. These are known as “National Pipe Tapered” or “NPT” threads. Mating MARINE and INDUSTRIAL thread forms can cause cross-threading, leaking and failure of the connection and is not recommended or approved by the ABYC.
Know your Thread
