AA Performance Products are put through a series of quality control tests to assure you of their reliability. AA pistons and liners are honed to exacting tolerances and balanced to one gram of each other. AA 90.5x69mm Hypereutectic pistons are composed of a high silicon alloy and are graphite coated to provide durability to fulfill your requirements. For use with a 69mm crank; machining of the case and the cylinder heads are required to fit.