Section 15 Base metals and articles of base metal 72 Iron and steel 72 18 Stainless steel in ingots or other primary forms; semi-finished products of stainless steel. 72 18 91 Of rectangular (other than square) cross section 72 18 91 00 Of rectangular (other than square) cross section Commodity Code Description 72 18 91 00 000 Of rectangular (other than square) cross section