Aftermarket Paslode and DuoFast Nailer Piston Driver. This is a generic replacement driver with o-ring for the Paslode F250S and DuoFast DF250-MC 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.