CBP may request mill test certificates or conduct physical measurement to verify the declared thickness. Because the boundary between 7210110000 (0.5 mm or more) and 7210120000 (under 0.5 mm) carries classification consequences, importers should ensure mill certifications state nominal and actual thickness clearly and retain those records for potential audit.

Heavier-gauge tinplate (0.5 mm and above) is primarily used in industrial and food-service packaging — large-format cans, paint and chemical containers, and aerosol components — where structural rigidity is required. Automotive and electronics applications that need thinner gauges typically fall under the sub-0.5 mm subheading.