5/16-18×1 1/4 six lobe pan thread cutting screw type 23 fully threaded zinc bake. Thread-cutting type-23 screws provide excellent chip clearance with minimum tightening torques. Steel: used in cast iron and zinc, aluminum die castings, and plastics. Stainless: material into which the screw is to cut threads should have a lower hardness. Pan head screws are a common style that can substituted in most applications for round, truss or binding heads.