8×1 phillips flat thread cutting screw type 25 fully threaded zinc bake. Thread-cutting type-25 screws provide excellent chip clearance. Steel: used in molded or through holes in plastics and other soft materials. Stainless: material into which the screw is to cut threads should have a lower hardness by 10-20 rockwell hardness. Flat head screws are used when protrusion of the fastener above the mating surface is unacceptable. Typically 100 degree flat or for fastening softer materials, 82 degrees flat.