Zinc at 99.99% purity or higher (Special High Grade, or SHG) commands a premium and is the standard for die-casting alloys and certain chemical applications. The subheading split at 790111 versus 790112 reflects this commercial distinction, and misclassification between the two can affect duty liability and trade statistics.

Subheading 790120 covers zinc alloys still in unwrought form — ingots, slabs, billets, and similar primary shapes not further worked. Once the alloy is cast, rolled, or otherwise fabricated into a specific article or semi-finished product, it moves to the appropriate downstream heading for zinc wrought products or articles of zinc.