This is VERY important !

The threaded part(s) of plumbing items are made to a British Standard Pipe Thread size (BSP).

BSP sizes don’t match up with what you would measure using a ruler, which can obviously cause some confusion.

For example a 3/4" BSP thread actually measures more like 1" with a ruler

We would suggest that you look at www.bspt.co.uk for more information.