These double claw clamps follow International Standards Organization (ISO) standards and fit flange sizes of NW-63, NW-80, NW-100, NW-160, NW-200, & NW-250. ISO 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. 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