Abstract: A container sidewall comprises a plurality of sections each section comprising an extruded aluminum post formed of a tubular rectangular tube having a pair of oppositely extending flanges coplanar with one of the tube broad sides and an aluminum plate riveted to each flange. An identical post interconnects the plates of adjacent sections. A reinforcing hat shaped rib is riveted to each plate midway between posts. The outer wall of the post tube is thicker than the inner wall which is the same thickness as the plates. The tube sides are thinnest to save weight. The plates are relatively thick to preclude damage during normal use. The tube is dimensioned to withstand transverse bending loads and bowing of the sidewalls to preclude damage in a rail car well.