This industry comprises establishments primarily engaged in shaping, molding, baking, burning, or hardening clay refractories, nonclay refractories, ceramic tile, structural clay tile, brick, and other structural clay building materials. Cross-References. Establishments primarily engaged in-- ? Manufacturing glass blocks--are classified in Industry 32721, Glass and Glass Product Manufacturing; ? Manufacturing concrete brick and block--are classified in Industry 32733, Concrete Pipe, Brick, and Block Manufacturing; and ? Manufacturing resilient flooring--are classified in Industry 32619, Other Plastics Product Manufacturing.