Backer-On cement screws are designed for attaching HardieBacker cement board and Rock-On cement board screws are designed for attaching Durock cement board to wood or light gauge steel studs. The patented serrated head design countersinks for a flush finish even at angle, providing a smooth surface for tile installation. The T25 star drive recess provides Stikfit for one handed installation. Climacoat corrosion-resistant finish prevents rust from bleeding into grout. Making it ideal for use in high-moisture areas such as bathrooms and kitchens. Backer-On and Rock-On cement board screws comply with ANSI standards for cement board installation as specified by cement board manufacturers. Cement board manufacturers require ANSI compliance in order to remain eligible for warranty.Serrated head – designed to drive flush even at an angleStar drive with T25 bit – provides Stikfit for easy one handed installation and eliminates cam outsHi-lo/single threads – starts quickly and drives smooth in cement boardsSharp points – offers immediate pick-up and eliminates the need to pre-drillClimacoat finish – corrosion-resistant for preventing rust from bleeding into tile