Thule Aeroblade Roof Rack Bar WindDiffuser is a textured surface on the t-slot cover that disturbs the airflow better than a smooth surface, greatly reducing wing noise. The sophisticated BoxBeam aluminum extrusion creates one of the strongest load bars in the market. SmartSlide is a molded measurement system providing a quick, no-hassle, tapemeasure-free foot installation. SmartSlide also covers the underbar slot to improve aerodynamics and noise diffusion. SwingBlade end cap pivots open to allow full access to the t-slot for easy accessory installs. AeroBlades work in conjunction with Thule feet and vehicle specific fit kit (sold separately). Please check the Thule fit guide for more information.