Replacement setup key for SRAM XX SL and XX Eagle T-Type AXS rear derailleurs. The setup key locks the cage in the correct position during installation so the derailleur lands in the right spot on the Full Mount, the same first step every T-Type install starts with. Keep a spare in the shop drawer. Fits XX SL and XX Eagle T-Type AXS rear derailleur cages Sold individually SRAM part 11.7518.104.009