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The Shimano 10T B / 12T D CS-M9100 is a two-piece replacement sprocket set designed to replace worn 10 and 12-tooth sprockets on a compatible Shimano 12-speed cassette.
Key Features
Construction and Design
The set includes a steel 10-tooth B-type sprocket and a 12-tooth D-type sprocket. These smaller cassette sprockets are frequently used in higher gears, and replacing them allows the most heavily worn parts of the cassette to be renewed separately.
Main Functions
The sprockets transfer chain force to the freehub body and provide the two highest gears in the drivetrain. Precisely shaped teeth and shifting profiles help guide the chain smoothly between adjacent sprockets.
Use and Compatibility
The set is designed for Shimano XTR CS-M9100 and CS-M9101 12-speed cassettes with 10–45T or 10–51T ranges. The manufacturer part number is Y1X498030, and installation requires a Micro Spline freehub body and a compatible Shimano 12-speed HG+ chain.
Additional Features
The 10 and 12-tooth sprockets are supplied together and must be installed according to their marked position and alignment indicators. When replacing them, the condition of the chain and remaining cassette sprockets should also be checked, as uneven wear may affect shifting performance.
Summary
The Shimano 10T B / 12T D CS-M9100 set is intended for repairing a compatible 12-speed cassette when its two smallest sprockets are worn. These original steel replacement parts help restore smooth shifting without replacing the complete cassette when the remaining sprockets are still serviceable.
