The FH-MT901-B Rear Hub is a Shimano non-series hub that comes with a Micro Spline freehub, making it compatible with the new XTR M9100 12 and 11-speed cassettes. It's a more economical option than the top-tier XTR hubs, but still offers the impressive durability and smooth rolling characteristics we typically associate with Shimano engineering. It's available in 28h or 32h configurations, uses serviceable cup and cone bearings, and is compatible with centerlock rotors only. For the most recent version of XTR, Shimano developed a new freehub body called Micro Spline that allowed them to move from an 11t to a 10t small cog on their cassettes while adding a 12th gear, increasing the gear range to a whopping 510% on their wide-range 12-speed cassette. The Micro Spline freehub body is made of aluminum instead of steel, saving weight while actually improving durability as the smaller and more numerous splines are designed to distribute force more evenly over a greater area, preventing the cassette from eating into the freehub body. As we noted earlier, this hub uses cup and cone bearings that are serviceable. That's definitely something you'll want to do on occasion in order to keep them running in top shape, and to continue enjoying greater strength and better load displacement than sealed cartridge bearings.