Classification into 690210 or 690220 requires that a single qualifying oxide group — magnesium/calcium/chromium for 690210, or alumina/silica for 690220 — exceeds 50% of the product's total composition by weight. If no single group clears that threshold, the article falls to the residual subheading 690290.

Certain refractory bricks originating from China may be subject to antidumping or countervailing duty orders, and some lines may carry Section 301 exposure. The applicable measure depends on the specific 10-digit tariff line and the country of origin, so importers should verify current orders with CBP or a licensed customs broker before entry.