Easily Identify a BSP Thread Size
Measure either A or B depending on if it is a male or female thread.
You can measure to the nearest millimetre as there is enough of a difference between each size to easily determine what you have.
Then compare to the data in the table below.
| | SIZE | A (mm) | B (mm) | TPI | |
|---|
| | 1/8” | 9.7 | 8.6 | 28 | |
| | 1/4” | 13.2 | 11.5 | 19 | |
| | 3/8” | 16.7 | 15.0 | 19 | |
| | 1/2” | 21.0 | 18.6 | 14 | |
| | 3/4” | 26.4 | 24.1 | 14 | |
| | 1” | 33.2 | 30.3 | 11 | |
| | 1.1/4” | 41.9 | 39.0 | 11 | |
| | 1.1/2” | 47.8 | 44.8 | 11 | |
| | 2” | 59.6 | 56.7 | 11 | |
| | 2.1/2” | 75.2 | 72.2 | 11 | |
| | 3” | 87.9 | 84.9 | 11 | |
| | 4” | 113.0 | 110.1 | 11 | |
| | 6” | 163.8 | 160.9 | 11 | |