Backer-On 1-5/8 in. Cement board screws are designed for attaching hardback or equivalent fiber cement Backer-On to wood or light gauge steel studs. Backer-On's patented serrated head design countersinks for flush seating at any angle, providing a smooth surface for tile. The star drive recess with T-25 bit provides steamfitter for one-handed installation. Backer-On screws feature a Climaseal corrosion resistant finish that prevents rust from bleeding into grout and are perfect for use in high moisture areas such as baths, showers, countertops, and floors. Conforms to ANSI A108.11 for cement board attachment. Backer-On screws can be installed with a standard impact or drill/driver and T-25 star drive bit (included with product) for cement board fastening done right. Backer-On #9 x 1-5/8-in Star-Drive Cement Board Screws (140-Count) | 23411