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

For 1-1/2, thread standard is BSP; threads per inch (tpi) is 11; thread pitch (mm) is 2.309; major (outside) diameter (mm) is 47.803; minor diameter (mm) is 44.845, recorded from its source on 2026-08-12.

- **Thread standard:** BSP _(our reading, not quoted from the source)_
- **Nominal size:** 1-1/2
- **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):** 47.803 _(verified: appears in the quote below)_
- **Minor diameter (mm):** 44.845 _(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

> 1½ | 11 | 2.309 | 1.479 | 47.803 | 46.324 | 44.845 |

## 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)

amesweb.info says major (outside) diameter (mm) is **47.803**, as of 2026-08-12.

> 1½ | 11 | 2.309 | 1.479 | 47.803 | 46.324 | 44.845 |

Source: https://amesweb.info/Screws/BSP-Thread-Chart.aspx

htsspares.com says major (outside) diameter (mm) is **47.80**, as of 2026-08-12.

> 1-1/2 Inch BSP | 47.80 mm / 1-3/4" | 11

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


## Source

- https://amesweb.info/Screws/BSP-Thread-Chart.aspx
- https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings

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/).