ACDelco 525-21 Specialty Heavy Duty Rear Shock Absorber Larger body allows for increased fluid capacity and cooler running for superior performance Bonded iron piston and compression head provides exceptional durability Extra-large 1-5/8 inch piston bore and 9/16 inch piston rod diameter for excellent stability and strength Heavy duty arc-welded end mounts for maximum strength and greater resistance to damage The super finished, chromed, piston rod provides anti-corrosion support, a more consistent wear surface, proper seal lubrication, and longer product life