Bolts are mechanical fasteners used to join two or more parts together, consisting of a head at one end and a threaded shaft with a nut on the other. They are available in various types, including hex bolts, carriage bolts, anchor bolts, eye bolts, and U-bolts, each designed for specific applications. Bolts are commonly made from materials like steel, stainless steel, brass, or aluminum, chosen based on factors like strength and corrosion resistance.