Hex washer head self drilling screws are made of 410 stainless steel and have a sheet metal thread with a self driller cutting (TEK) point to pierce through 20 to 14 gauge metals. * The higher the TEK number the larger the drill point to pierce heavier gauge metals. The heads use a hex nut driver 1/4, 5/16 or 3/8 depending on the size of the screw. * These screws are used in the exterior elements.