Found - New Possible Craftsman Code - CM
This socket was found mixed in a box with both C-xx (Snap-On) and BE (New Britain) socket tools. We are 99% confident the CM code is also produced by Snap-On.
The CM socket next to a C-xxx socket.
The two sockets reverse side / Craftsman stamp.
CM and C-xxx Broaching.
This is the label that is on the box with which the CM socket was found. It is not known whether the socket came with the box originally.