Threaded fasteners are among the most commonly used for assembling components due to the ease in which they can be installed and uninstalled as needed. There are three main types of threaded fastener; Bolts, Screws and Studs.
Bolts have a head on one end (this is usually a hex head) and are threaded on the other. They are generally used in conjunction with a nut (and sometimes a washer) to hold them in place.
Screws are similar to bolts in that they have a head on one end and a thread on the other. They key difference is thet screws are usually used to screw into an internally threaded hole. There are many different types of screws, such as Cap Screws, Machine Screws, and Woodscrews.
Studs are threaded on both ends, and therefore have no head. They are used to join two components with internally threaded holes together.
Fastener threads are standardised to two major standards: ISO (Metric) and ANSI (Unified). Threads can also be right-handed or left-handed, depending on the application. However, the majority of common fasteners are right-hand threaded.