The revolutionary machined design of the XX Cassette uses the same grueling manufacturing techniques that produced the PowerDome road cassette.With X-DOME, eight of the cogs are CNC-machined together out of a single block of billet steel, creating an incredibly lightweight, precise and strong cassette. It s a process that takes nine hours per cassette. You have never seen a cassette that looks like this.The open design aids in mud clearance, giving you cleaner shifting performance and longer component life.