The steel self-drilling screw with black oxide finish has a hex washer head and a hex drive. Steel is often used in applications where strength is the primary consideration. The black oxide finish offers mild corrosion resistance and lubricity. The hex washer head has six flat sides that wrenches can grip to turn from the side, enabling use when there is no space above the head for a screwdriver. The flange acts like a washer to increase the fastener's bearing surface and distribute the clamping force over a larger area, providing grip and reducing damage to mating surfaces.
Self-drilling screws, a type of self-tapping screw, are threaded fasteners that drill their own hole and thread it as they are installed. Usually only recommended for use with metal, self-drilling screws are available with wings that enable use when fastening wood to metal. The drill point length should be long enough to penetrate both materials being fastened before the threading portion reaches the material.