The M-series racks are single roof rails designed to mount to the top of enclosed trailers. Dual interior plates are used to connect the cross bar to the roof top by bolting through the mounting bases. The mounting bases contain two eye hooks that act as tie down points for cargo. Rubber gaskets are placed in between the mounting bases and roof top to prevent water leaks. Each cross bar comes with two 5" side supports that keep cargo contained to the racks. Zinc hardware comes with the durable steel cross bars and mounts. A protective black and white powder coating is applied to the racks to extend the cross bar life. Drilling is required for installation.