Superior Parts DBM83-04 Driver, Bumper, Ribbon Spring, O-Ring & Gasket Service Kit for Hitachi NR83A / A2 which includes SP 877-317 Aftermarket Cylinder Ring, SP 877-323 Piston Driver, SP 877-334 Aftermarket Gasket (A), SP 877-325 Aftermarket Gasket (B), SP 878-421 Aftermarket Ribbon Spring Set and SP 878-303 Piston Bumper. SP 877-323 Piston Driver: Aluminum is crimped into the unilok grooves of the shaft to prevent unscrewing. Hardened steel lock tite and micro-mechanically locked piston driver interface. never to unscrew. SP 878-303 Piston Bumper: Precision machined, virgin high density yellow color plastic framer bumper. WARNING: This product can expose you to chemicals which is [are] known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www. P65Warnings. ca. gov.