8109.21.00.00 - Containing less than 1 part hafnium to 500 parts zirconium by weight

This HTS category, 8109.21.00.00, specifically classifies unwrought zirconium and zirconium powders that contain a significant proportion of zirconium relative to hafnium. The defining characteristic is the weight ratio: for every 500 parts of zirconium, there are fewer than 1 part of hafnium. This precise quantitative threshold is the primary criterion for inclusion, indicating that the material is considered predominantly zirconium with minimal hafnium contamination.

It is crucial to distinguish this category from its sibling, 8109.29.00.00, which covers "Other" unwrought zirconium and powders. The sibling category would encompass materials that do not meet the specific hafnium-to-zirconium ratio outlined in 8109.21.00.00, meaning they either contain hafnium in greater proportions relative to zirconium or are not subject to this specific compositional test. Therefore, the key differentiator lies in the precise quantitative chemical composition.

As this HTS code represents a leaf node, there are no further subcategories within this specific classification. Consequently, the focus for classification purposes remains on the precise hafnium content as detailed in the description. Importers and exporters should ensure their documentation accurately reflects the weight percentages of zirconium and hafnium to ensure correct classification under this provision.