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.