These bigger ratios cost a few dollars more than the 11/21 and 11/23 because their low cogs require the use of a bit more titanium in the production process. The bottom 4 cogs on the Dura-Ace 10-Speed cassette are made from titanium -- unlike the 2 (or sometimes 3, depending on ratio) you got in the 9-speed era. These Ti cogs now get an improved surface treatment to give them a 30% increase in wear. They are compatible with all 8 and 9-speed Shimano hubs. Comes with a lockring. MSRP $219.99.