All three forms — dust, powder, and flakes — fall under 7903, which covers zinc in these finely divided forms regardless of particle size or production method. The distinction between dust and powder is not drawn at the heading level in this chapter, though specific tariff lines beneath 7903 may differentiate by form. Importers should verify the applicable 10-digit HTS line based on the physical form of the product.

Zinc die-castings and other articles of zinc are classified under 7907 (articles of zinc, NESOI) when they are identifiable as zinc articles. However, if a zinc component is a part of a specific machine, vehicle, or apparatus, the chapter notes for Section XV and the relevant product chapter may direct classification to that product's chapter instead. The general rule is that parts classified by their constituent material yield to more specific headings when the article's function is determinative.