These hex washer head self-tapping, self-drilling screws are a #8-18 x 3/4 in. size, supplied as a box of 100. This self-drilling screw is used in wood, fiberglass and metal, and it has a drill point that lets it drill its own hole in thin gauge steel. The sharp threads create their own mating thread when drilled into the material. No pre-drilled pilot holes are necessary.