A Brass bolt is a form of threaded fastener with an external male thread made from Brass. Bolts are generally used as connectors with applications in various mechanical and electrical industries. Bolts use a wide variety of head designs, as do screws. These are designed to engage with the tool used to tighten them. Some bolt heads instead lock the bolt in place, so that it does not move and a tool is only needed for the nut end.