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>