The threshold refers to the maximum cross-sectional dimension — effectively the diameter for round wire. Wire with a cross-section exceeding 6 mm falls under 740811; wire at or below 6 mm falls under 740819. For non-circular cross-sections, the greatest dimension is used.

Heading 7408 covers bare, uninsulated copper wire. Once copper wire is provided with an electrical insulating coating or sheath, it is classified in the chapter covering insulated wire and cable rather than here. The presence or absence of insulation is the key classification boundary.