With the change from Shimano's SD50 Di2 e-Tube wiring system to the slimmer, lower profile SD300 series released with 12-speed Dura-Ace R9250 series Di2 components the port and plug interface was made smaller. For some specific situations, such as connecting and SD50 from an 11-speed TT lever or brake level set-up to the SD300 series wiring or battery you will need this EW-AD305 Conversion Adapter. It also has e-bike applicability with the EP-8 / EP-800 Shimano motor/wiring systems. Each adapter has one SD50 port on one side and one SD300 port on the other, inline.