AJS M18s/G80s Piston 500cc Alloy Head 1950-56 +030. Compression Ratio 7.2:1. including gudgeon Pin, piston rings and circlips. Piston Clearance 0.12mm or 45thou. Pin Diameter 22mm. Hight 81mm. JP Piston Made in Australia. Please view ALL pictures. Measurements see pictures.