Connect 1-1/4 inch camlock coupling to 1-1/4" BSP parallel (G1-1/4 / BSPP)

A 1-1/4 inch cam-and-groove coupling has no thread of its own, so it reaches a G1-1/4 (parallel BSP (BSPP)) port through a same-size threaded camlock adapter: a Type A male adapter or a threaded coupler carrying the G1-1/4 thread on its back. That thread is a parallel, 55 degree form of 41.91 mm major diameter at 11 threads per inch and seals flat washer or bonded seal on the face; the cam end then mates to its opposite 1-1/4 inch camlock half.

The 1-1/4 inch cam profile and the G1-1/4 thread are two separate choices. A correct G1-1/4 back thread still leaves you with the wrong front if the half you mate to is not the matching 1-1/4 inch cam type, so confirm both the size and the A-to-F type before buying.