The Hex Washer Head TEKS are used for self drilling in thin gauge metals. They are used primarily in the Metal Fabrication and construction trades. Grade 410 Bright Hardened Stainless Steel used in self-drilling (Tek) screws is a Martensitic alloy containing 12% chromium BUT NO NICKEL. It is therefore somewhat less resistant to corrosive attack than the 300 Series grades. The reason for this is 300 series isn't hard enough to keep a drill point. It is magnetic and is hardenable by heat treatment which gives it the mechanical properties necessary to penetrate most metallic materials. It is recommended that these fasteners be used in thinner material. These fasteners are most popular for use in Aluminum.