How are plumbing threads measured – BSP or not BSP?

This one is quite simple, a BSP thread is British Standard Pipe, and BSPT thread is British Standard Pipe Tapered. You will note our earlier blog about how to measure a BSP thread, which is extracted below.

• A 3/8 Inch BSP thread measures approximately 5/8 inch in diameter
• A 1/2 Inch BSP thread measures approximately 3/4 inch in diameter
• A 3/4 Inch BSP thread measures approximately 1 inch in diameter
• A 1 Inch BSP thread measures approximately 1 1/4 inches in diameter
• A 1 1/4 Inch BSP thread measures approximately 1 1/2 inches in diameter
• A 1 1/2 Inch BSP thread measures approximately 1 3/4 inches in diameter…..etc

Essentially this is the same measurement rule for BSPT threads, the only difference is how the thread seals. On a BSP or parallel thread a fiber or rubber washer (and/or jointing compound if required) should be used on the male thread and then screwed into the female BSP thread until the shoulders of the male and female meet and then the seal is made by the washers. On a BSPT tapered thread, there are no shoulders to seal with a washer. The male thread should be wrapped several times around with PTFE jointing tape (and/or jointing compound) and then the male screwed into the female. As the threads are tapered they will get tighter and tighter until it is very difficult to screw further. The seal is therefore made with tape and sealant

A helpful tip is to wrap PTFE tape around the male threads in a clockwise direction so that when the thread is screwed in it does not unravel the PTFE of the thread.