BSP Thread Identification Chart
BSP – This is an abbreviation used for British Standard Pipe threads, and the size refers to the nominal bore (or internal diameter) of the steel pipe the thread was originally designed for, not the diameter of the actual thread.
Please measure your maximum (or major) thread diameter in millimetres and use the chart below to identify the BSP size you need.
| BSP Size | Actual Thread Diameter |
| 1/8" | 9.728 mm |
| 1/4" | 13.157 mm |
| 3/8" | 16.662 mm |
| 1/2" | 20.995 mm |
| 3/4" | 26.441 mm |
| 1" | 33.249 mm |
| 1 1/4" | 41.910 mm |
| 1 1/2" | 47.803 mm |
| 2" | 59.614 mm |
| 2 1/2" | 75.184 mm |
| 3" | 87.884 mm |