STRUCTURES (EXCLUDING PREFABRICATED BUILDINGS OF HEADING 9406) AND PARTS OF STRUCTURES (FOR EXAMPLE, BRIDGES AND BRIDGE-SECTIONS, LOCK-GATES, TOWERS, LATTICE MASTS, ROOFS, ROOFING FRAME-WORKS, DOORS AND WINDOWS AND THEIR FRAMES AND THRESHOLDS FOR DOORS, SHUTTERS, BALUSTRADES, PILLARS AND COLUMNS), OF IRON OR STEEL, PLATES, RODS, ANGLES, SHAPES, SECTIONS, TUBES AND THE LIKE, PREPARED FOR USE IN STRUCTURES, OF IRON OR STEEL