BSP Thread Guide

Measuring BSP threads.

Knowing the BSP thread size of a valve or pipe is of paramount importance when working with or maintaining any valve or pipeline equipment. Most regular users and qualified engineers will easily recognise a BSP valve port size, but either on occasion or as sound engineering practise will need to double-check these British Standard Pipe size measurements against size guides and charts.

However, novice plumbers, young engineers and DIY enthusiasts will discover that working out the actual BSP valve thread size can be quite a complicate process as the measured pipe diameter does not directly correlate to the standard thread terminology, and it can take some head scratching before being able to positively identify the port size in hand. For example, a 1" one inch BSP thread does not measure as one inch or 25mm across, but is instead more like 33mm!.

We have had instances where clients have measured the valve inlet/outlet port diameter with a ruler, ordered a valve, and then discovered that it is actually the wrong size. Then paid to ship the valve back, ordered the next size up with additional shipping charges and discover they are no better off and have to repeat the process a third time. With this in mind, we have made our valve thread picture size guide.

If it is helpful, you can also buy valves according to function and thread size here...

BSP British Standard Pipe Thread Sizes.

Nominal Pipe size 1/8" BSP, 28 threads per inch, major diameter 0.4 inches, outside diameter 10mm.

Nominal Pipe size 1/4" BSP, 19 threads per inch, major diameter 0.5 inches, outside diameter 13mm.

Nominal Pipe size 3/8" BSP, 19 threads per inch, major diameter 0.7 inches, outside diameter 17mm.

Nominal Pipe size 1/2" BSP, 14 threads per inch, major diameter 0.8 inches, outside diameter 21mm.

Nominal Pipe size 3/4" BSP, 14 threads per inch, major diameter 1 inch, outside diameter 26mm.

Nominal Pipe size 1" BSP, 11 threads per inch, major diameter 1.3 inches, outside diameter 33mm.

Nominal Pipe size 11/4" BSP, 11 threads per inch, major diameter 1.7 inches, outside diameter 42mm.

Nominal Pipe size 11/2" BSP, 11 threads per inch, major diameter 1.9 inches, outside diameter 48mm.

Nominal Pipe size 2" BSP, 11 threads per inch, major diameter 2.4 inches, outside diameter 60mm.

Nominal Pipe size 21/2" BSP, 11 threads per inch, major diameter 3 inches, outside diameter 75mm.

Nominal Pipe size 3" BSP, 11 threads per inch, major diameter 3.5 inches, outside diameter 88mm.

Read our FAQ section for more information and guidance.