How to measure a BSP Thread

Identifying BSP Threads

One of the most frequent problems that we have found our customers run into is the identification and measurement of pipe threads.

In Great Britain BSP British Standard Pipe threads are commonly used. These are either parallel (BSPP) which normally seal on a washer or 'O' ring seal, or tapered (BSPT) which taper along their length and normally seal by two mating threads.

How to measure your thread:

Use a tape rule (or vernier gauge) to measure across the outside of the male thread. Note that a thread that measures 1/2" is not a 1/2" BSP thread.

Using the table below we can see that a thread measuring 1/2" is actually a 1/4" BSP thread. Similarly, a thread that measures 1" is actually a 3/4" BSP thread.

Other Threads

In Europe Metric (DIN) pipe threads are common on German machines. These generally have a 1.5mm thread pitch, although this can vary. Smaller sizes can be 1.0mm thread pitch, and larger sizes can be 2.0mm thread pitch. Other variations occur. French equipment often have GAZ fine threads with a 24 degree cone.

In North America NPT, JIC and ORFS pipe threads are common. Some NPT threads are similar to BSPT threads so if in doubt check origin of part.

In Japan JIS tapered and parallel threads are common and are interchangeable with the respective BSPT and BSPP threads, although the 30 degree cones might be inverted.