Wheat flour (heading 1101) and certain other milling products are subject to TRQ treatment, meaning a lower in-quota duty applies up to a set volume, with a higher over-quota rate above it. Importers must track quota fill levels and file appropriate TRQ claims at entry.

Heading 1108 covers extracted starch compounds and inulin regardless of source grain, while 1109 is limited to wheat gluten — the protein fraction separated during wheat starch production — whether dried or undried. A product's principal constituent (starch vs. protein) and source material determine which heading applies.