Brass is a copper-zinc alloy, while bronze is primarily a copper-tin alloy — though the term 'bronze' is sometimes used commercially for other copper alloys. For customs classification at the HTS 10-digit level, the specific alloying elements and their weight percentages determine the subheading. Importers should provide a certified mill test report or material data sheet showing the full chemical composition to support correct classification.

At the SITC 5-digit level, this heading covers copper alloys broadly regardless of form. However, at the HTS 10-digit level used for US customs entry, the physical form — unwrought ingot, cast billet, wrought rod, or other — typically determines the specific subheading and can affect the applicable duty rate. Importers should specify both the alloy composition and the physical form when working with a broker to determine the correct tariff line.