Gauges feature and 4 1/2" phenolic case for superior chemical and burn resistance, and a solid front case with a blow-out back for safety. Dry case gauge ensures no leakage, disposal, or environmental issues with any liquid fill. The case ring on all gauges is threaded polycarbonate. The back cover for all dry case gauges is polypropylene and for liquid filled and hermetic cases the cover is polycarbonate. Gauge is easily recalibrated.