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, but does not include the tightening thumb handle. Use your existing thumb handle from your existing mount instead.
For mounting instructions see link here.