The folks at Jardine tell us that one of the most popular alloys found in motorcycle parts is 6061-T6 aluminum. In the 1950s the Aluminum Association adopted a four-digit numerical classification system for aluminum. The first digit, the six, states that this alloy contains aluminum, magnesium, and silicon; giving the alloy good formability, corrosion resistance, and strength. (If the first digit were a one, the metal would be more than 99 percent pure aluminum.) The zero means that special controls to limit particular impurities within the alloy were not incorporated (not a concern in motorcycle applications). The final two digits identify the particular alloy within the aluminum, magnesium, and silicon group. The -T6 designates aluminum alloys that have been thermally treated and artificially aged for additional hardness. So, to sum it all up: 6061-T6 aluminum is a light, strong, corrosion-resistant alloy that is ideally suited for motorcycling.