BBB derailleur pulleys RollerBoys Ceramic 12-T.Equipped with low-friction ceramic bearings for ultra-smooth gliding and exceptional longevity.Narow Wide serrated profile for optimum chain retention.Special lubrication with light ceramic oil for greater smoothness.Composite material supplied by EMS Swiss in glass-fiber blend (40%).Compatible with SRAM 1X11 system.With them, you´ll never be done rolling!.