Chains are a series links connected to form one continuous piece with the structure of a rope in that it is flexible and strong. Chains are available in a variety of shapes, sizes and thickness, and are often manufactured from various metals. Chains are relatively simple to install and can provide security in a variety of ways such as door chains to prevent access, restraints to restrict movement of an item and secure it, and keychains to keep keys together and stop from getting misplaces.