Shimano Di2 E-Tube 4 Port Junction B - (SM-JC40 or SM-JC41)

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The Shimano Di2 Junction B box is the center of the e-tube Di2 system. All of the component and battery wires meet here before running out to their respective components. All of the wires that connect to the junction box use the same connector to make assembly that much easier. Choose the SM-JC40 External box if you are running your wires on the exterior of the frame or choose the SM-JC41 internal box if you are running your wires inside your frame.