Piston Kit - XLManufactured from high strength, T 5, heat treated, 390 hypereutectic aluminum alloy. Allow a tighter fit and longer piston and ring life. Diamond machined pistons are held to plus or minus one gram weight and less than one half thousandth inch (. 0005") tolerances from piston to piston. Each kit contains two pistons, pins, spiral lock pin clips and Hastings moly rings. Replacement piston rings and pin lock rings available separately. KB pistons can