NPT Pipe Threads
NPT threads are tapered and seal by deformation. Always verify the correct drill and use a sealant appropriate to the service.
Common sizes
- 1/8-27 → R drill (.339 in)
- 1/4-18 → 7/16 in
- 3/8-18 → 37/64 in
- 1/2-14 → 23/32 in
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National Pipe Taper basics, taper geometry, and common tap drills.
Machine-readable reference
Structured metadata for formulas, tags, canonical status, and future diagram support.
Slug
npt-pipe-thread
Category
Threads & Fasteners
Canonical
Yes
Updated
4/23/2026
Units
inch
Tags
NPT, pipe, tapered
Source
Machinery's Handbook, 31st ed., Pipe Threads
NPT threads are tapered and seal by deformation. Always verify the correct drill and use a sealant appropriate to the service.
Source: Machinery's Handbook, 31st ed., Pipe Threads