Enduro rear derailleur jockeys are made from Delrin plastic, the highest grade bearings, and machined aluminum bearing covers, all made in the USA. The machined Delrin jockey will outlast any other on the market. Rear derailleur jockeys spin 7 times faster than your BB making the XD-15 ceramic bearings all the more critical for making sure all your power drives you down the road. The smooth action pulley also increases shifting performance and reduces overall drivetrain wear. These rear derailleur jockey sets work with Shimano 9100 Road rear derailleurs and contain XD-15 sealed cartridge bearings.