Section 15 BASE METALS AND ARTICLES OF BASE METAL 73 ARTICLES OF IRON OR STEEL 73 05 406.4 MM, OF IRON OR STEEL. 73 05 31 OTH.TUBES & PIPES, EXT. DIAMETER>406.4MM, LONGITUDINALLY WELDED, OF IRON/. Commodity Code Description 73 05 31 00 OTH.TUBES & PIPES, EXT. DIAMETER>406.4MM, LONGITUDINALLY WELDED, OF IRON/.