Section 15 Base metals and articles of base metal 73 Articles of iron or steel 73 05 Other circular tubes and pipes,external diameter >406.4mm, of iron or steel 73 05 20 Casing of a kind used in the drilling for oil or gas 73 05 20 00 Casing of a kind used in the drilling for oil or gas Commodity Code Description 73 05 20 00 000 Casing of a kind used in the drilling for oil or gas