Aftermarket Hitachi Stapler Piston Driver. This is a generic replacement driver with o-ring for the Hitachi N5008AC / N5008AC2 / N5008ACP 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.