Motor Unit for Internal Geared Hub
This Motor Unit is meant to be used with the S705 / S7050 Internal Geared Hubs - both 8 and 11 speed versions.
It is because of this part that you can use Di2 to shift Internal Geared Hubs. It has one E-Tube Port and connects to the rest of the Di2 system. You can then use regular Di2 shifters to control your hub.