Piston assembly (complete with piston, rings, gudgeon, circlips) to suit Norton ES2 , Model 18, OHV 1948 to 1958. 79mm + 0.40 oversize. Italian made by Gandini (GPM). Can be used for pre 1948 motors with large flywheels if the skirt length is reduce by machining. Original Norton part number: 3790 - Piston assembly with gudgeon pin A3/160; A3/161; A3/162; A3/163; A3/164