Wood screws are perhaps the single most common type of screw is a wood screw. Machine Screw. A machine screw, as the name suggests, is a type of screw that's used in machining applications. Others are - Sheet Metal Screw, Twinfast Screw and a Security Screw. A screw is a type of fastener typically made of metal and characterized by a helical ridge, known as a male thread. Screws are used to fasten materials by the engagement of the screw thread with a similar female thread, internal thread in the matching part. Screws are often self-threading also known as self-tapping, where the thread cuts into the material when the screw is turned, creating an internal thread that helps pull fastened materials together and prevent pull-out. There are many screws for a variety of materials; those commonly fastened by screws include wood, sheet metal, and plastic.