# 5 1/2 — Plumbing fitting and pipe thread standards

For 5 1/2, thread standard is BSPP; threads per inch (tpi) is 11; thread pitch (mm) is 2.309; major (outside) diameter (mm) is 151.130; minor diameter (mm) is 148.173, recorded from its source on 2026-08-12.

- **Thread standard:** BSPP _(our reading, not quoted from the source)_
- **Nominal size:** 5 1/2 _(verified: appears in the quote below)_
- **Threads per inch (TPI):** 11 _(verified: appears in the quote below)_
- **Thread pitch (mm):** 2.309 _(verified: appears in the quote below)_
- **Major (outside) diameter (mm):** 151.130 _(verified: appears in the quote below)_
- **Minor diameter (mm):** 148.173 _(verified: appears in the quote below)_
- **Thread angle (degrees):** 55 _(our reading, not quoted from the source)_
- **Governing standard:** ISO 228-1 _(our reading, not quoted from the source)_

## What the source says

> BSPP G 5 1/2 | 5 1/2" | 11 | 2.309 | 151.130 | 149.651 | 148.173

## Source

- https://www.machiningdoctor.com/charts/bsp/

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/).