Deore XT RD-M8100 Rear Derailleur-Offers fast and shockless shifting thanks to HYPERGLIDE technology-The low-profile design includes a bumper added to the derailleur pulley cage-Shimano Shadow RD technology reduces chain slap and creates a quieter drivetrain-Includes large 13t pulley-Drivetrain is silent in all gear positions with decreased rear derailleur and chain tension in low gear-Medium cage derailleur for 12-speed drivetrain