Material: This bike derailleur pulley adopts quality aluminum alloy and ceramic material. It uses anti-rust and anti-corrosion materials to ensure long-term use, and resistant anodized machined bicycle jockey wheel ensure normal working Performance: this bike guide roller pulley not only reduces drag and improves cycle efficiency but is also very durable. Additional accessories: The bicycle rear derailleur use ceramic bearings, for center bolt derailleurs which protect the bike. These pulleys run on smooth ball bearings. Compatibility: This bicycle derailleur accessories is compatible for most of rear derailleur on the market and adjust to 7/8/9/10 speed. After-sales: If our bicycle rear derailleurs has any problems that do not meet your expectations, please feel free to contact use, will make it right Bicycle Rear Derailleur