BSA DBD Gold Star Pre Unit 500cc Kolben +060. 86. mm. BSA Unit Gold Star 500cc +100 GPM Slipper 86.5 mm 9.5:1 Piston Clearance 0.12mm or 45thou Can be used on BSA B50 as a +80 Pistonwith Piston Rings, Circlips and Gudgeon Pinplease look at all pictures