Section 15 Base metals and articles of base metal 73 Articles of iron or steel 73 05 Other tubes and pipes (for example, welded, riveted or similarly closed), having circular cross-sections, the external diameter of which exceeds 406,4 mm, of iron or steel 73 05 20 - Casing of a kind used in drilling for oil or gas Commodity Code Description 73 05 20 00 - Casing of a kind used in drilling for oil or gas