Heat treated tool steel 6150 Rockwell hardness 50-52 Aerospace grade number 2024 Aluminum piston Mechanically locked piston driver interface Compatible with Max CN70 Coil Nailer Aftermarket Compatible with Max Nailer Piston Driver. This is a generic replacement driver with o-ring Compatible with Max CN70 coil nail 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.