Phillips, Truss, Thread Cutting Screws, Type 23 Thread. 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. Truss head screws are weaker than pan or round heads but preferred in applications where minimal clearance exists above the head. Modified truss heads offer low clearance and an extra large bearing surface. Commonly used to attach metal lathe to metal studs.