Phillips, Flat, Thread Cutting Screws, Type 1. Thread-cutting Type-1 threaded screws are used in steel sheets, sructural shapes, special alloy steels, cast iron, brass or plastics. Stainless steel 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.