If you've purchased an 11/21 or 11/23 Campagnolo 10-speed cassette, they supply you with an 11t-specific lockring. If you've purchased one in any other ratio, they supply no lockring. Why? Because every 10-speed Campagnolo rear hub and prebuilt rear wheel was supplied with a lockring that functions with 12t and 13t high gear cassettes. These lockrings are non-interchangeable, i.e. the 11t lockring won't work with cassettes that start with a 12t or 13t cog. They're made from steel with a 27mm O.D.
These Campagnolo Cassette Lockrings are for 10-speed cassettes (all 11-speed Campagnolo cassettes come with lockrings). The actual weights of the Campagnolo Cassette Lockring: 11 tooth is 13g. 12/13 tooth is 17g.