These single claw clamps follow International Standards Organization (ISO) standards and fit flange sizes of NW-63, NW-80, & NW-100 ISO flanged vacuum fittings are commonly used to build process vacuum plumbing and systems for industrial applications. They also can be used for Edwards Bolt Down Vacuum Pumps. The fittings are quick to assemble using single 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 clamps are made of Stainless Steel