This guide covers standard specification for round, square, rectangular, and special shape, electric-resistance-welded mechanical tubing, either zinc-coated (galvanized) after welding or produced from aluminum-coated, zinc-coated (galvanized), zinc-iron alloy-coated (galvannealed), or aluminum-zinc alloy-coated steel sheet. Low-carbon steels and other carbon steels shall conform to the required chemical composition for carbon, manganese, phosphorus, and sulfur. The steels shall conform to elemental tolerances for product analysis. Wall thickness tolerances for premetallic coated as-welded tubing and diameter tolerances for metallic-coated round tubing shall be provided.

1.1 This specification covers round, square, rectangular, and special shape, electric-resistance-welded carbon steel mechanical tubing, either zinc-coated (galvanized) after welding or produced from aluminum-coated, zinc-coated (galvanized), zinc-iron alloy-coated (galvannealed), 55 % aluminum-zinc alloy-coated, or zinc-aluminum-magnesium alloy-coated carbon steel sheet. Tubing for use as electrical conduit (EMT) or intermediate metallic conduit (IMC) is not covered by this specification.

1.1.1 The product is available in various grades based on chemical requirements (Sections 5 and 9).

1.1.2 The product is available in various Types (Section 3).

1.2 This specification covers mechanical tubing with outside diameters or maximum outside dimensions ranging from ¹/₂ to 15 in. [12.7 to 380.0 mm] and wall thickness from 0.028 to 0.180 in. [0.70 to 4.60 mm]. Indeterminate wall thicknesses may be ordered. In those cases the more stringent tolerances of Tables 3, 4, 5, 6, 12 and 13 shall apply.

1.3 When sizes within the ranges listed above are ordered, all other requirements of the specification shall be met.

1.4 This specification is expressed in both inch-pound units and in SI units; however, unless the purchase order specifies the applicable M specification designation (SI units), the inch-pound units shall apply. The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.