Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of npt / nps. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
NPT is tapered at 1:16 and seals metal-to-metal on the thread flanks with a sealant. NPS is parallel and seals on a gasket or O-ring against a shoulder. They share the same basic thread form and the same nominal sizes, so the designations look alike and the fittings behave completely differently.
NPTF is a dry-seal variant where the crest and root are controlled to interfere, allowing a seal without compound.
Common misuse
Threading an NPS fitting into an NPT port. It will go part-way in and then leak, which is worse than not fitting at all.