Hitachi Nailer Piston Driver. This is a generic replacement driver with o-ring for the Hitachi NR65AK, NR65AK2, NR65AK(S) 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 unilok grooves of the shaft to prevent unscrewing. never to unscrew. 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.