The rail extrusion can be ordered with a 1" radius machined out of the back side to accomodate welding the rail to a 1" round aluminum rail. Order the quantity of feet needed on the checkout page there will be a custom cut list field that the lengths of the rails can be added. Example if you need a 4 foot and a 6 foot rail purchase 10 feet of machined rail and enter the lengths needed in the custom cut box on the checkout page.