Self-Drilling Screws, also known as Tek screws, eliminate the need for a pre-drilled hole. The length of the drill point determines the material thickness which the screw can reliably penetrate. When selecting a self-drilling screw design, it is important to consider the material thickness and type of materials to be joined. These #8 x 1/2 stainless teks are great to use in environments that are damp. These work great on gutters.