A handy person from BOULDER COLORADO says:
January 22, 2016
NUMBER ON BACK IS R-40-28 PAT...3204. 1 & 1/16" OPENING FOR WOOD GUIDE AND THEN SAME SIZE FOR BOTTOM GUIDE. LOOKS LIKE Plastic back bearing for drawers. Slot measures 1-1/8" x 5/16". Printed on the product: Ronthor Reiss Corp: R-40-28. Attach with furniture staples, fasteners not included. See SWISCO product code 32-118 for this drawer guide with installation holes.
Paul from SWISCO responded:
January 25, 2016