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.
Strap wrench
The strap or chain can have various forms. Some straps are made of polymers, and are smooth, highly flexible, non-marring, high-friction straps. (Before the era of commercial polymers, the straps were of leather or rubber.) Other straps are bands of spring steel, moderately flexible, slightly firmer and more likely to mar than the polymer variants. The chains tend to be of the roller chain type (like a bicycle chain).