Heading 6902 covers refractory articles used in construction — bricks, blocks, and tiles that form furnace walls or linings. Heading 6903 covers non-constructional refractory shapes such as nozzles, retorts, muffles, and plugs that serve a functional role within a process rather than forming a structural element. The article's intended use and physical form are the primary classification guides.

If the article contains more than 50% free carbon by weight, it falls under subheading 690310 regardless of other mineral content. Articles that do not meet that carbon threshold are then assessed for alumina or silica dominance (690320) or classified to the residual subheading 690390.