These requirements cover aluminum and stainless steel electrical metallic tubing (EMT) and elbows in trade sizes 3/8 ?C 4 (12 ?C 103) for use as a metal raceway for the installation of wires and cables in accordance with the National Electrical Code. The values in parentheses are metric designators of tubing. Tubing provided with an exterior coating of zinc or a zinc-based@ nonmetallic@ or other alternate corrosion-resistant material and an interior coating of an organic or zinc material@ is covered by the Standard for Electrical Metallic Tubing ?C Steel@ UL 797.