What are screws most commonly made of?
Screw
A screw is a type of fastener, in some ways similar to a bolt (see Differentiation between bolt and screw below), typically made of metal, and characterized by a helical ridge, known as a male thread (external thread). Screws are used to fasten materials by digging in and wedging into a material when turned, while the thread cuts grooves in the fastened material that may help 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.
List of screw drives
A U-drive screw has a helical thread with an angle acute enough to be driven by a hammer, and thus has a domed head with no means of turning it. These are most frequently driven into plastic.