Wolf Tooth Components GC 42 Cog and 16T Cog Bundle: For SRAM 11-36 10-speed cassettes, Black SRAM GC42s are not compatible with 2011 or older SRAM rear derailleurs Compatible only with the following SRAM 11-36 and 12-36 cassettes: PG-1030, 1050, 1070 and the XG-1080 Remove the 14T cog on the XG-1080 instead of the 17T Compatible only with the following SRAM 10 Speed Cassettes: X5 11-36T (PG-1030), X7 11-36T (PG-1050), X9 11-36T (PG-1070), X0 11-36t(XG - 1080) - Remove the 14t rather than the 17t Per Wolf Tooth, the GC 42 is not compatible with 2011 or older SRAM rear derailleurs due to the position of the upper jockey wheel. The best ways to tell the vintages of your rear derailleur