Aftermarket Hitachi Nailer Piston Driver. This is a generic replacement driver with o-ring for the Hitachi NR90AD and NR90ADPR strip nail guns. This comes with a patent-pending locking mechanism which will not allow the driver to unscrew from the piston. Aluminum is crimped into the unlock grooves of the shaft to prevent unscrewing. 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.