Shimano 105 RD-R7150 Di2 Rear Derailleur - 12-Speed For 2x12 Speed Direct Mount Black. The Shimano 105 RD-R7150 Di2 12-speed rear derailleur completes a shift in the blink of an eye with its high-performance motor and optimized link structure. This is the hub of the Shimano Di2 system with the charging port indicator LEDs adjustment switches and more integrated into a compact package.Low-profile Shimano Shadow RD design reduces damage from contact and fallsReceive the wireless shifting signal from the shift leverCheck the battery level and Bluetooth/ANT pairing success with your cycle computer/smartphone/tabletAllows selection of preferred shift mode and view adjustment mode information (if you wish to tweak or tune your rear derailleur)Smartphone/tablet connectivity via E-TUBE PROJECT