LIAG^® inline sight glasses are designed for visual inspection of media inside pipes and/or inspection of pigs in product recovery systems. The Borosilicate glass inside the housing is fixed without any tension and does resists hard pressure and vibration shocks.inline sight glasses are designed for visual inspection of media inside pipes and/or inspection of pigs in product recovery systems. The Borosilicate glass inside the housing is fixed without any tension and does resists hard pressure and vibration shocks.