The message
from Matt contains these words:

Is it 1/2 " bsp or metric?

BSP is an ISO standard thread, which makes it officially a metric thread.

Are you *really* sure of that?

My now rather old reference states:

"British Standard pipe threads are recognised by ISO and are maintained
in the inch system with fractional designations for pipe joints."

The dimensions in the tables are metric apart from TPI.

--
Roger Chapman