I bought this thinking I was going to need it for my headrest mount, but I have yet to use it....figures. It is made by Manfrotto and is a quick change plate adaptor, which you can either screw in with a 1/4"-20 threaded screw or the standard screw that comes on tripods and monopods, etc. It is all metal and kinda heavy (compared to others), so this sucker will NOT break.
I paid over $40 for this at New York camera. I am looking for $35 + Shipping (couple bucks). It is all in the original package with manual.