Piston Kit - 38.95 mm - Cobra 50 Kit includes piston, ring set, wrist pin and circlips, Gravity cast aluminum alloy with 18% silicon to increase resistance to wear and decrease thermal distortion , Coated skirt eases break in, decreases wear and aids in lubrication, Piston rings are either nitride or chrome plated, Wrist pin is nitride coated, providing a hardened, wear resistant bearing surface