Inspection glasses are devices used to observe the internal material conditions of containers and equipment. They are safety accessories and should be inspected regularly. They are categorized by shape into round and rectangular inspection glasses. By function, they are divided into viewing and illuminated inspection glasses. Structurally, they include lined and unlined, with neck, with cover, double safety, insulated, scraper-equipped, flushing-equipped inspection glasses, as well as those suitable for powdered materials.