# 5/8 — Plumbing fitting and pipe thread standards

For 5/8, thread standard is BSP; threads per inch (tpi) is 14; thread pitch (mm) is 1.814; major (outside) diameter (mm) is 22.911; minor diameter (mm) is 20.587, recorded from its source on 2026-08-12.

- **Thread standard:** BSP _(our reading, not quoted from the source)_
- **Nominal size:** 5/8
- **Threads per inch (TPI):** 14
- **Thread pitch (mm):** 1.814
- **Major (outside) diameter (mm):** 22.911 _(verified: appears in the quote below)_
- **Minor diameter (mm):** 20.587
- **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

> 0.9020 | 22.911

## Sources disagree

More than one authority states this, and they do not state the same
thing. Both are reproduced with the source each came from.

### Major (outside) diameter (mm)

en.wikipedia.org says major (outside) diameter (mm) is **22.911**, as of 2026-08-12.

> 0.9020 | 22.911

Source: https://en.wikipedia.org/wiki/British_Standard_Pipe

htsspares.com says major (outside) diameter (mm) is **22.99**, as of 2026-08-12.

> 5/8 Inch BSP | 22.99 mm / 7/8" | 14

Source: https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings

trimantec.com says major (outside) diameter (mm) is **22.4**, as of 2026-08-12.

> -10 (5/8) | 14 | 22.4 | 0.88 | 20.3 | 0.80

Source: https://trimantec.com/blogs/t/thread-identification-guide


## Source

- https://en.wikipedia.org/wiki/British_Standard_Pipe
- https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
- https://trimantec.com/blogs/t/thread-identification-guide

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/).