The Box Three Rear Derailleur simplifies the features found on the Prime 9 Box One and Two rear derailleurs making for a fully featured wallet friendly rear derailleur. Including a Limited Slip Clutch, Sealed bearing pulleys and a solid construction Box Three Rear derailleurs are compatible with 11-46 and 11-50t derailleurs making it one of the most versatile derailleur offerings for Prime 9.