Shimano JC41 Di2 Internal Frame Junction Box 4-Port

Considered a B-junction in Di2 parlance, the Shimano e-Tube Di2 SM-JC41 Junction Box is the central connector for internally routed Di2 e-Tube systems. Wires from the front and rear derailleurs, cockpit area, and battery all plug into the 4-port SM-JC40 junction, which integrates the inputs for full connectivity. Remember that a single wire is run from the cockpit junction box down to the SM-JC41, as the cockpit junction A integrates the shifters. Features  4-port junction box for internally wired Di2 e-Tube set-ups; integrates the ported wires Can connect e-Tube wires from: front and rear Di2 derailleurs, cockpit junction, battery Sit inside lower downtube/BB area on most frame designs Composite material; sealed Color: Black Weight: 5 grams Shimano part # ISMJC41