# 2-1/2 — Plumbing fitting and pipe thread standards

For 2-1/2, thread standard is NPT; threads per inch (tpi) is 8; thread pitch (mm) is 3.1750; major (outside) diameter (mm) is 73.0250; thread angle (degrees) is 60, recorded from its source on 2026-08-12.

- **Thread standard:** NPT _(our reading, not quoted from the source)_
- **Nominal size:** 2-1/2
- **Threads per inch (TPI):** 8
- **Thread pitch (mm):** 3.1750
- **Major (outside) diameter (mm):** 73.0250 _(verified: appears in the quote below)_
- **Thread angle (degrees):** 60 _(our reading, not quoted from the source)_
- **Governing standard:** ASME B1.20.1 _(our reading, not quoted from the source)_

## What the source says

> 2.875 | 73.0250 |

## Source

- https://en.wikipedia.org/wiki/National_pipe_thread

Last verified: 2026-08-12. Review by: 2028-08-11.
Part of [Plumbing fitting and pipe thread standards](https://referencesource.org/plumbing-fitting-thread-standards/).