... > SECTION XV - BASE METALS AND ARTICLES OF BASE METAL > CHAPTER 73 - ARTICLES OF IRON OR STEEL > 7308 Structures (excluding prefabricated buildings of heading 9406) and parts of structures (for example, bridges and bridge-sections, lock-gates, towers, lattice masts, roofs, roofing frameworks, 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 > Other > Solely or principally of sheet > Panels comprising two walls of profiled (ribbed) sheet with an insulating core