Reese Towpowers 4 inch square style is popular due to the simplicity of the installation mounting post. This item is fast and easy to install and mounts using two studs that attach right to the frame of the trailer. The grounding of the lights is instantly accomplished when mounting onto a steel trailer. Not only does this light comply with the Department of Transportation rear lighting requirements, but it also meets the rear reflex reflector requirements., Lot of 1