SRAM Apex Eagle Rear Derailleur - 12-Speed Long Cage 52t Max Black D1SRAM Apex Eagle Rear Derailleur 12 Speed Long Cage 52t Max Black D1. The SRAM Apex Eagle rear derailleur quietly and quickly shifts across their 12 speed Eagle cassettes while 1x specific chain retention technology keeps the chain where it needs to be. Its the best of SRAMs road and mountain bike innovations in one package. Compatible with 50t and 52t Eagle cassettes Works with SRAM 12 speed mechanical Apex and Eagle shifters For use with Eagle 12