wossner piston kit yamaha yz250f std a 8957da 1Enhanced Piston Pin Oiling Slots, Radial Boss Machining, and Annoular Grooves For Improved Wrist Pin Lubrication, Lightweight Piston With A Tight Piston Wall Clearance For A Quiets Running Engine, Skirt Coated for Reduction and Impriction and Improvd Seal and Oil Control, Double Bridged Forging Design Where Noted, Kit Includes Piston, Rings, Wrist Pin and Pin Locks