Manufacture of structural components, steel or other metal, of bridges, tanks, smoke stacks and buildings; metal doors and screens, window frames and sashes, metal staircases and other architectural metal work; metal sections for ships and barges; boiler shop products; and sheet metal components of buildings, stovepipes and light tanks. The assembly and installation at the site of pre-fabricated components into bridges, tanks, boilers, central air conditioning and other sheet-metal systems by the manufacturer of these components which can not be separately reported, is to be included in this group, along with the main manufacturing activity.