Lowered rear axle plates are raw cast steel and threaded 3/8"-18 UNC for fender brace and sissy bar mounting and 3/8"-24 UNF for 1936-1972 Big Twin axle adjusters. They lower the bike 1 1/2" (38mm). Axle mounts accept 3/4" axle, mounts will need material added to fit tight into rectangular swing arm tubing. Recommended plug weld from sides as well. Use axle and spacers or 3/4" threaded rod for alignment purposes. Welding and fabrication required for installation. Cut original rectangular swing arm to desired length. Fabricator must cut swingarm and reweld lowering axle plates in place and check fender clearance.