Rear drawer track socket with dowel pins
A handy person from Pittsburgh says:
January 20, 2015
It has "R1" stamped on it. The dowels/pins fit into holes in the back of the cabinet.
Paul from SWISCO responded:
January 22, 2015
We do not have this exact type of socket. Our 32-018 could be a match, as it is meant to accommodate a 7/8" x 3/8" track, but it screws in. Could you use this as a substitute?