Connect 1-1/2 inch camlock coupling to 2-1/2" BSP tapered (R2-1/2 / BSPT)

A 1-1/2 inch cam-and-groove coupling reduces up to the larger R2-1/2 port with a reducing threaded camlock adapter: the cam end stays 1-1/2 inch while the back thread is R2-1/2 (tapered BSP (BSPT)), a tapered, 55 degree thread of 75.184 mm major diameter at 11 threads per inch that seals on the thread flanks with PTFE tape or paste. Because the camlock is two nominal sizes away from the thread, this is the reducing version of the adapter, carried as one part rather than a same-size adapter stacked on a separate R2-1/2 reducer.

The cam end mates only to its opposite 1-1/2 inch camlock half, so the R2-1/2 back thread does not change what fits the front. Match the cam type (A to F) to the half you are joining and confirm the back really is R2-1/2 and not the same size in a different standard before buying.