Screws, BoltsScrews and bolts are mechanical fasteners that are used to hold or join two or more objects together. Screws have a spiral groove, or thread, cut into their surface, which allows them to be inserted into and tightened in a pre-drilled hole in a piece of material. Bolts, on the other hand, typically have a thread on the outside of their body, and are inserted through a hole in the material and tightened using a nut. Both screws and bolts are available in a variety of different sizes, styles, and materials to suit different applications and design requirements. They are an essential component of many different types of mechanical systems and assemblies.