# 2½ — Plumbing fitting and pipe thread standards

For 2½, thread standard is NPT; threads per inch (tpi) is 8; thread pitch (mm) is 3.175; major (outside) diameter (mm) is 73.03; 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:** 2½ _(verified: appears in the quote below)_
- **Threads per inch (TPI):** 8 _(verified: appears in the quote below)_
- **Thread pitch (mm):** 3.175 _(verified: appears in the quote below)_
- **Major (outside) diameter (mm):** 73.03 _(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

> 2½ | 8 | 0.125 | 3.175 | 2.875 | 73.03

## Source

- https://www.geminivalve.com/bsp-thread-vs-npt-fitting/

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/).