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. Guaranteed never to unscrew.