# 1¼ — Plumbing fitting and pipe thread standards

For 1¼, thread standard is NPT; threads per inch (tpi) is 11½; thread pitch (mm) is 2.20878; major (outside) diameter (mm) is 42.16; 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:** 1¼ _(verified: appears in the quote below)_
- **Threads per inch (TPI):** 11½ _(verified: appears in the quote below)_
- **Thread pitch (mm):** 2.20878 _(verified: appears in the quote below)_
- **Major (outside) diameter (mm):** 42.16 _(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

> 1¼ | 11½ | 0.08696 | 2.20878 | 1.66 | 42.16

## 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/).