shimano ultegra di2 junction box one color, internal/sm-jc41 shimano the shimano ultegra di2 junction box is what is referred to as the b junction. this is the point in the wiring system where all the component pieces converge. it's a crucial item along with the five required wire sections to operate your ultegra di2 drivetrain.the ultegra di2 junction box is available in two configurations -- internal and external. the internal style is designed to be located inside the bike frame (usually inside the down tube, tucked in from a hollow bottom bracket shell). the external version is designed to be fixed on the outside of the bottom bracket shell, usually fastened to the cable guide.<br /><br /><b>product features</b><ul style="list-style-type: disc; margin-left: 25px;"><li>material: plastic</li><li>type: </li><li>crankset compatibility: 2 x 10</li><li>compatible components: shimano ultegra di2</li><li>weight: </li><li>recommended use: ditching your mechanical tethers</li><li>manufacturer warranty: 2 years</li></ul>