This 13-tooth upper and 19-tooth lower OSPW System has been platform proven at races like Paris Robaix, Strada Bianche and CX World Cups. The system is built for gravel and cross disciplines and meets the needs for durability, low friction and longevity. The four spring tension settings allow customised setup based on ride conditions, and the handbuilt OSPW System offers custom molded carbon fiber cage for lightweight and durability. CeramicSpeed OSPW Systems reduces friction 35-40% over stock pulley configuration. Compatible with the 2X-specific RX820 and RX825 derailleurs. If you are using a 1x you can use a 36T cassette maximum. Note: Only the H (high) spring tension hole should be used with the RX825 Di2 derailleur. In the box: Complete OSPW X for Shimano GRX RX-820 2x12 system CeramicSpeed Oil for Pulley Wheel Bearings, 15 ml. dropper bottle