For hot-rolled products, the 4.75 mm boundary separates heading 721114 (4.75 mm or more thick) from 721119 (under 4.75 mm thick). Getting the measured thickness right at entry is critical because the two subheadings can carry different duty rates and Section 232 treatment.

The defining criterion is width: 7211 covers flat-rolled nonalloy steel less than 600 mm wide, while 7209 and 7210 cover products 600 mm or more wide. Additionally, 7211 is limited to uncoated, unclad material — surface-treated narrow strip of the same width falls under heading 7212.