The 10-51T offering provides 510% of range, making it the most versatile cassette in the DEORE XT family. It is also MICRO SPLINE-compatible and built with steel and alloy cogs to optimize weight and durability. The 9-45T offering provides 500% of range, optimizing it for compact drivetrains with limited gear sacrifice. This cassette is still MICRO SPLINE-compatible and built with steel and alloy cogs to optimize weight and durability.Key Features:·510% Range (10-51T Cassette)The widest gear range and most frame compatibility of all DEORE XT cassette options.·Compact Drivetrain (9-45T Cassette)When specified with smaller chainrings and the mid-cage DEORE XT rear derailleur, the 9-45T DEORE XT cassette provides a lightweight, ground-clearing option with a no-sacrifice 500% range.·Freehub CompatibilityCS-M8200 is compatible with the MICRO SPLINE freehub body standard.·Build MaterialsThe strategic use of steel and alloy ensures the CS-M8200 cassette is robust enough to provide confidence to any style of rider.