Campagnolo is a bit of a funny company. If you purchase an 11-21 or 11-23 cassette, they supply you with an 11t-specific lockring. If you purchase any other ratio cassette, they supply no lockring. Why? Because every Campy rear hub and prebuilt rear wheel comes supplied with a lockring that functions with a 12t and 13t high cassette. These lockrings are non-interchangeable, i.e. the 11t lockring won't work with cassettes that start with a 12t or 13t cog. Made from steel with a 27mm O.D.