These Overpressure centering rings include an overpressure ring and can be operated at 5-100 psig, and a replaceable Viton® O-ring rated to 180°C max. These Over Pressure centering rings follow International Standards Organization (ISO) standards and have a flange size of NW-80, ISO80, LF80. ISO flange vacuum fittings are commonly used to build process vacuum plumbing and systems for industrial applications. The fittings are quick to assemble using double claw clamps and a centering ring (please see top right figure - click to enlarge). The Viton® centering ring contains a rubber/elastomeric o-ring. The ISO standard sizes for large flanges are NW-63, NW-80, NW-100, NW-160, NW-200, NW-250, NW-320, NW-400, NW-500, NW-630. These vacuum fittings are made of corrosive resistant stainless steel.