Self-Drilling and Tapping Screws are made of high-quality steel and are specially heat treated. The drill point has been incorporated into the screw in the familiar twist drill design. These screws drill their own hole - form mating threads - fasten securely and can be used in steel, plastics, composite materials, wood plus various laminates. Determine total thickness of the material to be drilled then choose No. 2 or No. 3 point to allow complete drilling. Zinc plated.