Connect 2" camlock (cam-and-groove) coupling to 1-1/2" NPT (National Pipe Taper)

A 2 inch cam-and-groove coupling reduces down to the smaller 1-1/2-11.5 NPT port with a reducing threaded camlock adapter: the cam end stays 2 inch while the back thread is 1-1/2-11.5 NPT (NPT), a tapered, 60 degree thread of 48.26 mm major diameter at 11.5 threads per inch that seals on the thread flanks with PTFE tape. Because the camlock is one nominal size 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 1-1/2-11.5 NPT reducer.

The cam end mates only to its opposite 2 inch camlock half, so the 1-1/2-11.5 NPT 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 1-1/2-11.5 NPT and not the same size in a different standard before buying.