Distributor rotor arm (points), suits BSA Triumph twins, Norton Dominator 88 99, Indian, Enfield, AJS. Matchless, 3TA T21 5TA TIGER100; 6T THUNDERBIRD For the 18D2 (40573) type distributor. Fits many British twinds 1957-63? Original Part Number: 423486 - distributor rotor arm