Athena Aprilia 50 40mm Bore 50cc Standard Bore Cylinder Kit w/HeadThe Standard Bore cylinder kit developed by Athena guarantees the same performance as the original spare parts, extreme reliability and optimal smoothness as a result of the lightweight aluminum cylinder, the barrel with nickel silicon coating, and a piston designed to reduce further friction. The kit includes the high quality aluminum cylinder with standard bore, the complete piston with the piston pin and rings, and all the necessary gaskets.