This is an upgrade to replace the existing mounting pin on the Focus Mount.  This is a machined part - much more robust than the molded pin that comes standard with the Focus Mount - made from 6061 aluminum, that will fit both a Junior Socket (1-1/8") from a Combo/Junior Stand, as well as a Baby Pin (5/8") from a C-Stand. Includes the two screws needed for mounting as well as the tightening screw handle. 
For mounting instructions see link here.