"Disc has a 1in. bore and keyway for live axle mounting. Fits our #13833 brake assembly shown, not included. U.S.A. Bore Diameter in. 1, Application Brake disc, Disc Diameter in. 8, Keyway in. 1/4. 1 3/4in. Hub diameter 3/4in. Collar 1/8in. Thick 1/4in. Square keyway in a 1in. bore Works with brake assembly Item # 113833"