Piston Kit - YZ125/X - 57.95 mm The piston is heat-treated with a T-5 hardening and tempering cycle, The piston skirt is coated with a high-tech Molybdenum Disulphite coating for faster break in time and increased piston life, Cast piston is gravity-cast aluminum alloy (not forged) with 18% silicone content, Big bore piston increases engine's displacement, torque, and peak horsepower, Piston kit includes piston, rings, wrist pin and circlips