This is a brand new gearbox transmission sprocket.
Part # 57-1917, T-1917
Sprocket teeth: 18
Chain size: 530
Chain Pitch: 5/8″ X 3/8″
Fits: Triumph unit 650cc with 4 speed from 1964-72
Triumph T150, BSA A75 with 4 speed from 1968-72