The 2nd generation Di2 e-Tube wiring system from Shimano has the SD300 designation. These wires and connectors are thinner than the SD50 generation. if you need to join two SD300 wires to create a longer length, you will need this EW-JC302 Di2 SD300 2-Port Junction Box, which is actually a simple looking connector with internal ports on both ends that accept the SD300 connectors and provide the proper, seamless bridge for the power and data transfer rates of the SD300 wires. Use of TL-EW300 Cable Plug Tool is required to preserve connector integrity as the thinner wires and connectors are more difficult to manage by hand.