The US tariff lines under 721391 separate tire cord wire rod (7213913011), cold-heading quality rod (7213913015), and welding-quality rod (7213913020) as distinct lines, with a residual NESOI line (7213913093) for other non-tempered grades under 14 mm. Classification depends on the steel's chemical composition, cleanliness specifications, and the declared end use supported by mill certificates. Misclassification between these lines can affect AD/CVD scope determinations, as some orders are grade-specific.

Lines 7213914500 and 7213916000 split the under-14 mm diameter category by carbon content — above and below 0.6% carbon respectively — for rods that do not fall into the tempered or specialty-grade lines. High-carbon rod (above 0.6%) is used for spring wire and high-strength applications, while lower-carbon grades serve general wire drawing. The carbon content on the mill certificate is the controlling document for this distinction.