Both pipes and their fittings (elbows, junctions, traps) fall within heading 6906 when made of ceramic materials. The heading text explicitly includes pipe fittings, so a ceramic elbow or junction piece does not need to be classified separately under a fittings heading — it stays with 6906 as long as it is ceramic.

Heading 6903 covers refractory tubes and pipes designed for high-temperature industrial processes (furnace components, thermocouple sheaths). Heading 6906 covers ceramic pipes and conduits used for fluid conveyance — drainage, sewerage, and chemical transport — at ambient or moderate temperatures. The intended service environment and the article's refractory character are the distinguishing factors.