Shimano's SM-JC41 is the Di2 Junction B for internal routing: a small 4-port E-Tube hub that sits inside the frame near the bottom bracket and links the derailleurs, battery and front junction.

• Model: SM-JC41 (Junction B, internal type)
• E-Tube ports: 4
• Wire: E-Tube EW-SD50
• Weight: approx. 4 g
• Compatible: Dura-Ace Di2 9070/R9150, Ultegra Di2 6770/6870/R8050, GRX Di2 RX815, XTR M9050/XT M8050 Di2, Alfine Di2
• Wires sold separately