AEST pulley wheel is equipped with a high quality hybrid ceramic cartridge bearing. The advantages of using a ceramic bearing in the rear derailleur's pulleys are the most dramatic of any other bicycle bearing system. This is due to the high speed at which the pulleys spin. Each pulley is machined from light and strong 7075 aluminum and anodized with laser cut logos. Brand AEST Model YPU09A-07 Features High Speed High rigidity Long use-life Low heat Low heat dilating rate Corrosion resistance Non-magnetic Color RedBlack Material AL7075 CNC processing Ceramic bearing Functions Rear Derailleur Pulley Inner diameter: 5mm Best Use CyclingMountain bikingRoad cycling Packing List 1 x Rear derailleur pulley