Aftermarket Hitachi Coil Nailer Piston Driver. This is a generic replacement driver with o-ring for the Hitachi NV65AH / NV65AH2 coil nail guns. This driver comes with O-ring (880-311) but does not include the plastic piston ring (878-691). This piston ring goes on top of the under sized o-ring. 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.