The Hillman Washer Head Self-Drilling Screw is used in wood, fiberglass and metal, and it possesses a drill point enabling it to drill its own hole in thin gauge steel. The sharp threads on these self-drilling screws create their own mating thread when drilled into the material. Perfect for roofing construction, these self-drilling metal screws have a neoprene washer that provides a water-tight seal, and prevents corrosion between surfaces. These drill into the roof to remove material Have a neoprene washer that provides a water tight seal Have a ceramic finish that is corrosion-resistant Recommended for use for treated woods 12 x 1-1/2 in. self-drilling screws Self drilling screws designed for power driving wood or metal to metal Drill point drills its own hole, taps mating threads and fastens firmly in one operation Zinc finish for moderate corrosion protection No need to pre-drill a hole 20 self-drilling metal screws per pack