Shimano EW-JC304 Di2 Junction Box - 4 Ports Use With EW-SD300. Shimano Di2 Frame Junction Box

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

Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/