These mounts were designed to attach a Rola V-Tex/Vortex Roof Rack directly to the factory roof rails of a 3rd Gen (1996-2002) Toyota 4Runner. These eliminate the factory crossbars and allow it to be mounted much lower than with the original mounting hardware. This uses M3 screws to attach the top section to the bottom. Heat set threaded inserts also need to be melted into the bottom parts so the screws have something secure to thread into. The bolts that attach the bottom to the roof rails are M6-1.0. Stainless Steel hardware is recommended so it doesn't rust.