Backer-On is a manufacturer that specializes in cement board fasteners. These fasteners attach HardieBacker or equivalent fiber cement backerboard to wood or light gauge steel studs. It has a serrated head design that countersinks, allowing for a flush seating at any angle and a smooth surface for tile. The star drive bit is a T-25 bit and comes with all screw packages and is also available to be ordered in case extra is needed. Rock-On Cement Board Screws are self drilling, self tapping, and Climacoat corrosion resistant to prevent rust from bleeding into the tiles grout.