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What's the difference between NPT and NPS thread?

NPT (National Pipe Thread) and NPS (National Pipe Straight) have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered, and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys.

Tapered pipe threads are commonly found on ends of the pipe, nipples, and fittings (i.e. couplings, elbows, tees, etc.).

Note: Sharply angled threads are critical to tight joints with no leaks. Thread sealant or tape is typically required to complete the seal.

Straight pipe threads need a gasket or O-ring to create a seal.

While NPT and NPS threads will engage, they do not seal properly with each other.

Title: What's the difference between NPT and NPS thread?
Description: A comparison of NPT (National Pipe Thread) and NPS (National Pipe Straight).
Published: 3/13/2015
Last Edited: 1/23/2023

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