Shimano EW-SD50 E-Tube wires. FEATURES: Frame grommets for E-tube internal-wiring compatible frames are sold separately, see Shimano Frame Grommet Kit Electronic Shifter Extra Parts Ultegra Di2 wires utilize Shimano's e-tube technology; e-tube is a two-prong system and is NOT cross compatible with Dura-Ace 7970 Di2 wiring All e-tube wires may be used for internal or external applications