ISO (International Standards Organization) flanged 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 304 stainless steel.