Whispbar WB401 Saddle Roller Kayak Carrier - Rooftop Kayak Boat Rack ONLY fits crossbars with top t-slot channel Integrated SmartLoad rollers for easy rear roll-on loading Aerodynamic profile reduces noise and decreases drag up to 70 percent Carries a boat up to 80 lb / 36 kg Patented SmartFill technology allows for fast and seamless install of Whispbar accessories