No introduction needed. Dura Ace is synonymous with super high-end road. The CS-9000 11 speed rear cassette uses a Super Narrow HyperGlide design, has titanium and nickel-coated steel cogs and a carbon spider. It is optimized for 11 speed and is NOT compatible with HG 8-10sp freehubs. Precision shifting, durability and an incredibly low weight are what it's all about.