The Hylex RS is a full hydraulic disc brake system for drop bar bikes. It sports an integrated master cylinder in the ergonomically shaped lever body while the drilled out lever blade shaves weight as well as improves grip.. This brake is for single speed aficionados, the rider who wants simplicity without sacrificing braking performance. Using our Hylex Di2 Adapter Kit, this system can be used with a Di2 drivetrain. Flat mount only.