With its Beam Spider construction, the updated XTR M9101 12-speed cassette shaves weight while increasing Shimano's MTB gearing range another gear. Using Shimano's new Micro Spline freehub body and Hyperglide+ tooth profile, these 10-45t and 10-51t cassettes deliver the best MTB shift experience available. New for Spring 2021! This is the updated version of the CS-M9100 XTR cassette. Details: Model No: CS-M9101-12 Series: XTR M9100 Cog sizes: 10-45t:10-12-14-16-18-21-24-28-32-36-40-45t Cog sizes: 10-51t: 10-12-14-16-18-21-24-28-33-39-45-51t Compatible chain: HG 12-speed Number of speeds: 12 Finish: Anodized Compatibility: All Micro Spline freehub body's Rear Derailleur: 10-45t: XTR RD-M9100-GS, Medium cage Rear Derailleur: 10-51t: XTR RD-M9100-SGS, Long Cage