This U.S. industry comprises establishments primarily engaged in manufacturing glass by melting silica sand or cullet and making pressed, blown, or shaped glass or glassware (except glass packaging containers). Cross-References. Establishments primarily engaged in-- ? Manufacturing flat glass--are classified in U.S. Industry 327211, Flat Glass Manufacturing; ? Manufacturing glass packaging containers in glassmaking operations--are classified in U.S. Industry 327213, Glass Container Manufacturing; ? Manufacturing glass wool (i.e., fiberglass) insulation--are classified in U.S. Industry 327993, Mineral Wool Manufacturing; ? Manufacturing glassware from purchased glass--are classified in U.S. Industry 327215, Glass Product Manufacturing Made of Purchased Glass; and ? Manufacturing fiber optic cable from purchased fiber optic strand--are classified in U.S. Industry 335921, Fiber Optic Cable Manufacturing.