While many of today's framesets feature internally routed and integrated Di2 e-Tube wiring capability, the popularity of the most precise and reliable electronic shifting system is still a great upgrade for framesets without internal routing, and Shimano supports this with a variety of external set-up specific parts. The Shimano e-Tube Di2 SM-JC40 External Junction Box mounts underneath the bottom bracket, where a derailleur cable guide is usually located. The included screw (2 length options) threads into the hole that is normally used for the cable guide mounting screw. It becomes the central connector for Di2 e-Tube systems. Wires from the front and rear derailleurs, cockpit area, and battery all plug into the 4-port SM-JC40 junction, which integrates the inputs for full connectivity.