This is the CMM probe shank MS1. MS1 shank for Brown and Sharpe, Bridgeport, Elm systems, Fanamation, Giddings and Lewis, ITP, Poli, Portage Machine, Tesa and Zettmess CMMs.
It is part number: #M-1041-2146.
Shanks are used to mount the probe head to the quill of the machine.There are a range of shanks suitable for all Renishaw manual and motorised probe heads (except PH6 and MH20), as well as the TP1 probe. There is also a range which is specific to the PH6and MH20. The correct shank must be chosen to suit the mounting facility of your CMM.