● Not sure what you need? Give us a call on 01384 913150 or use our   contact form  to get in touch! ● Orders placed before 12pm generally processed and dispatched the same day (Monday to Friday) We are currently experiencing high demand so this may not always be possible - for time critical orders please contact us for availability ● Not sure what you need? Give us a call on 01384 913150 or use our contact form to get in touch!

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!