The CeramicSpeed Oversized Pulley Wheel System is the secret to increasing the efficiency of your derailleur through friction reduction. This version is optimized for Shimano Dura-Ace or Ultegra systems. This version features coated bearings, leading to outstanding efficiency and a very long life of like-new performance. This coating makes them 75 percent harder than steel. A carbon cage keeps the weight low and the wheels protected while the included oil helps you maintain operation. The upper pulley has 13 teeth while the lower has 19. This version features blue wheels to fit in with the theme of your favorite bike. The CeramicSpeed Oversized Pulley Wheel System helps you get the most out of your high-end Shimano Di2 road groupset.