Piston Kit - 53.94 mm - Yamaha YZ125/X Piston is heat treated with a T-5 hardening and tempering cycle, Piston skirt is coated with a high-tech Molybdenum Disulphite coating for faster break-in time and increased piston life, Gravity-cast aluminum alloy (not forged) with 18% silicone content, Cast OE piston, Kit includes piston, rings, wrist pin and circlips