Self-drilling screws are manufactured for use in wood, fiberglass and metal. They possess a drill point which enables the screw to drill its own hole in thin gauge steel; no pre-drilled holes are necessary. The sharp threads create their own mating thread when drilled into the material, and provide a stronger grip to your surface. Perfect for roofing construction, these screws have a neoprene washer that provides a water-tight seal, and prevents corrosion between surfaces. Zinc. 100-piece per package.