NPT
Glossary · Threads & Fits
At a glance
- Category /
- Threads & Fits
- Also called /
- national pipe thread, pipe thread
- Related /
- 3 terms
- Source /
- Written in the shop
NPT is the American tapered pipe thread standard, where the thread itself tapers so that the joint seals as the threads are pulled tight together.
Also called: national pipe thread · pipe thread
In practice
Unlike a straight thread that needs a gasket or O-ring, an NPT joint seals on thread flank contact, usually assisted by sealant or tape. Because it is tapered, engagement depth rather than a defined stop determines how far it goes in.
Why it matters
Overtightening NPT splits fittings and cracks housings, because the taper acts as a wedge. Correct assembly is measured in turns past hand tight, not by feel.
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