SRAM 6-Bolt Disc Bicycle Rear Hubs
About SRAM - "Incremental enhancements. Perpetual improvements. Revolutionary Innovation. When advancements are continuously made to every attribute of every component, the result is overall performance that is simply second to none. And to real cycling enthusiasts, there is nothing more gratifying then achieving the ultimate ride. And the best part is we just keep making it better. This is what SRAM is all about."
This should correspond to the type of brakes you have on the bike.