SRAM RED ETAP Mid Cage Rear Derailleur: The SRAM RED eTap rear derailleur executes shifts the moment you demand it, with military precision. Wirelessly. It’s easy to set up, clean in appearance and delightfully uncomplicated. Mechanical necessities such as a carbon pulley cage, ceramic pulley bearings, and high polished alloy artfully blend with proprietary electronic advancements to deliver a 239g* shifting wonder. *including battery