Why would you need the Shimano E-Tube Di2 5-Port A-Junction Box? Well, because it's two better than the 3-Port A-Junction Box. It's also really important if you want to have shifters on both your base bar and aero bars on your TT bike and you want them BOTH to work. It also features a plug on the side for charging an internal battery if you have one, so that's cool. Isn't technology great?!
designed for clean installation under the stem
5 ports allow for the connection of 4 shifters and the rest of the system; best used for Tri bikes
has a plug on the side for charging an internal battery if so equipped
not compatible with 7970 Di2 systems