11T Bicycle Rear Derailleur Bearing Pulley 4mm 5mm 6mm MTB Bike Bearing Guide Roller Aluminium Alloy Bike Derailleur Accessories. Style: 11T. Enhanced Chain Stability: The deep tooth design of this bicycle rear derailleur jockey wheel minimizes chain slippage, enhancing the stability and response speed of the gear-shifting system for a seamless ride.