shimano ultegra di2 internal routing junction box shimano shimano's e-tube di2 junction box (also known as the b junction) connects all your component and battery wires to make assembly much easier. it's a crucial item along with the five required wire sections to operate your ultegra 6770, ultegra 6870, or dura-ace 9070 di2 shift system. the e-tube di2 junction box is available in two configurations: internal (sm-jc41) and external (sm-jc40).