The steel self-drilling screw with black oxide finish has a pan head and a square drive. Steel is often used in applications where strength is the primary consideration. The black oxide finish offers mild corrosion resistance and lubricity. The pan head has a flat top and short vertical sides with a rounded top edge. The square drive resists slippage better than a Phillips or slotted drive.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.