BSP Measurement guide
Aaron on 6th Sep 2024
Measuring threads and matching sizes can be a headache - especially for a DIYer putting things together for the first time, getting the right fitting for the job can be daunting!
When measuring a thread - it's best to use this conversion chart below to find out what BSP size fitting you actually need - as you'll see - it's not exactly what you imagine when a 3/4" fitting measures around an inch!
| SIZE | TPI | Thread Size EXT (mm) | Thread Size INT (mm) |
| 1/8" | 28 | 9.728 | 8.566 |
| 1/4" | 19 | 13.157 | 11.445 |
| 3/8" | 19 | 16.662 | 14.95 |
| 1/2" | 14 | 20.955 | 18.631 |
| 5/8" | 14 | 22.911 | 20.587 |
| 3/4" | 14 | 26.441 | 24.117 |
| 7/8" | 14 | 30.201 | 27.877 |
| 1" | 11 | 33.249 | 31.77 |
| 1 1/8" | 11 | 37.897 | 34.939 |
| 1 1/4" | 11 | 41.91 | 38.952 |
| 1 3/8" | 11 | 44.323 | 41.365 |
| 1 1/2" | 11 | 47.803 | 44.845 |
| 1 3/4" | 11 | 53.746 | 50.788 |
| 2" | 11 | 59.614 | 56.656 |
| 2 1/4" | 11 | 65.71 | 62.752 |
| 2 1/2" | 11 | 75.184 | 72.226 |
| 2 3/4" | 11 | 81.534 | 78.576 |
| 3" | 11 | 87.884 | 84.926 |
| 3 1/4" | 11 | 93.98 | 91.501 |
| 3 1/2" | 11 | 100.33 | 97.372 |
| 3 3/4" | 11 | 106.68 | 103.722 |
| 4" | 11 | 113.03 | 110.072 |
| 4 1/2" | 11 | 125.73 | 122.772 |
| 5" | 11 | 138.43 | 135.472 |
| 5 1/2" | 11 | 151.13 | 148.172 |
| 6" | 11 | 163.83 | 160.872 |
I hope this comes in handy when choosing the right products - as always, if you find yourself stuck and need a bit of guidance, you're always welcome to give us a call!