Metals are among the most important construction materials the human race has ever used; in fact, a number of prehistoric eras are named after the most commonly used metals of the time, such as the Bronze Age and the Iron Age. The Industrial Revolution allowed for the mass production of steel for the first time, and this completely transformed construction for buildings, vehicles, and weapons of war. Today, steel mills around the world can make thin sheet metal products of all sorts, and many grades of steel exist, from 304 stainless steel to high-yield steel for making I-beams. Some thin sheet metal pieces may be made of aluminum instead, another valuable metal, or perhaps they are made of copper and brass or related alloys. When might steel be used, and in what situations should thin sheet metal be made of alloys instead?