BSA Unit & Pre-Unit Models "Quick Detachable" Rear Hub Rubber Washer. If your Rebuilding your BSA Rear Wheel, we Highly Recommend changing this Rubber Washer! Most of the time, some owners Fail to change them simply because the part then was not available! Outer Diameter measures approx 3", I.D. approx 2 3/8" & Width is approx 1/2". Fits BSA Unit Twins (Lightning Rocket, Lightning, Royal Star, Spitfire, Etc) from approx 1964-1970 with the "QD" Rear Hub. Fits BSA Unit Singles (Victor, B44, B25, C25, Shooting Star, Etc) from 1967-1970. Fits Triumph TR25W Trophy from 1968-1970. Also fits most BSA Pre-Unit Twins & Singles (Goldstar, Goldenflash, B31, B32, Etc) up to approx 1957 with the Correct "Quick Detachable" Rear Hub only.