The GC line of cassette extender cogs allows you to modify your 10-speed cassette into a wide range cassette. To achieve the optimal shifting.   Compatibility Compatible Sram cassettes: PG 1030, 1050, and 1070 - 11-36T and 12-36T / X0 11-36t(XG - 1080) - Remove the 14T rather than the 17T. Compatible with all 10-speed rear derailleurs and chains. Can be run in 2x configuration with a long cage rear derailleur. Note: You may need a longer chain that you currently have your bike   Hub compatibility These fit very tight on certain Stan’s No Tubes hubs like the 3.30 and the Easton X4 hubs. With a little filing and some, grease they will go on.. These are specifically designed for use with SRAM cassettes. The clocking, or rotational orientation, between SRAM and Shimano cassettes are much different so optimal shifting cannot be achieved unless the design is optimized for each separately..