These Retaining Rings For NW-63 with nonrotatable flanges follow ISO-LF standards and have a flange size of NW-63. These Retaining Rings prevent Optional Fastener Flanges from slipping through the bolt ring and are used with nonrotatable flanges with clearance bolt holes. Large Flange fittings are commonly used to build foreline vacuum plumbing and process systems. The fittings are quick to assemble with a double claw clamp or a single claw clamp for tapped bored flanges and a centering ring forming the vacuum seal between the connecting flanges (please see top right figure - click to enlarge). The standard sizes for Large Flanges are LF63, LF80, LF100, LF160, LF200, LF250, LF320, LF400, LF500, LF630. LF is an ISO (International Standards Organization) standard but is often called LF, NW, or Large Flange.