HTS Code 6903.90 - Retorts, crucibles, mufflers, nozzles, plugs, supports, cupels, tubes, pipes, sheaths, rods and other refractory ceramic goods (excluding those of siliceous fossil meals or similar siliceous earths, those of heading 6902, containing 50% carbon or containing 50% by weight of alumina [Al203] or a mixture or compound of alumina and silica [SiO2])