Abstract: A method for producing a U shaped seat back frame from a single extruded blank. The blank's cross section is nearly circular, but with a pair of short, flattened off crests that create a pair of concentric arcs, in cross section. Over a length of each end of the blank, a rectangular cross section, solid mandrel is inserted between the crests and the arcs are flattened against the mandrel. The arcs are flattened into wider side walls, while the crests move apart, without deformation, to create narrower and stiffer walls of a rectangular cross section. Lastly, the U blank with flattened ends is bent into a U shape, creating an upper beam with a nearly circular cross section, and legs with truly flat and rectangular lower ends.