2-Stroke piston kits are gravity cast aluminum alloy (not forged) with 18% silicone content, which produces an extremely light but very strong piston. 4-Stroke pistons are forged from 2618 aluminum for superior strength and durability. 4-Stroke high-compression pistons improve power and torque across entire rpm range. 4-Stroke big-bore pistons increase engine's displacement, torque and peak horsepower. All pistons are heat treated with a T-5 hardening and tempering cycle. All pistons skirts are coated with a hi-tech molybdenum disulphide (MoS2) coating for faster break-in time and increased piston life. Standard pistons and rings are O.E.M. replacements. Kits include piston, rings, wrist pin and circlips. Std, 63.94 mm