Shimano Dura-Ace/Ultegra Di2 SM-JC41 Internal Wire Junction Box

This is the Shimano Ultegra Di2 Internal Junction Box. This box is referred to as the junction box "B" on a Di2 build. The SM-JC41 is for use with internal wiring setups and is the main centre of e-tube Di2 systems.. Frame Junction Box connects via SD50 E-tube wires to four different points: front derailleur, rear derailleur, cockpit junction box and battery mount
. All Di2 components on the bicycle require the same firmware version
. Using Di2 components with different firmware versions may cause malfunctions