for single-ridge guide. MIL-spec flanges have designations of the form UG-xxxx/U where the x'''s represent a variable-length catalogue number, not in itself containing any information about the flange. These standards are works of the U.S. government, and are freely available online from the U.S. Defense Logistics Agency. IEC International Electrotechnical Commission (IEC) standard IEC 60154 describes flanges for square and circular waveguides, as well as for what it refers to as flat, medium-flat, and ordinary rectangular guides. IEC flanges are identified by an alphanumeric code consisting of; the letter U, P or C for unpressurizable (plain cover), pressurizable (with a gasket groove) and choke (with both choke gasket grooves); a second letter, indicating the shape and other details of the flange and finally the IEC identifier for the waveguide. For standard rectangular waveguide the second letter is A to E, where A and C are round flanges, B is square and D and E are rectangular. So for example UBR220 is a square plain cover flange for R220 waveguide (that is, for WG20, WR42), PDR84 is a rectangular gasket flange for R84 waveguide (WG15, WR112) and CAR70 is a round choke flange for R70 waveguide (WG14, WR137). The IEC standard is endorsed by a number of European standards organizations, such as the British Standards Institution. EIA The Electronic Industries Alliance (EIA) is the body that defined the WR designations for standard rectangular waveguides. EIA flanges are designated CMR (for connector, miniature, rectangular waveguide) or CPR (connector, pressurizable, rectangular waveguide) followed by the EIA number (WR number) for the relevant waveguide. So for example, CPR112 is a gasket flange for waveguide WR112 (WG15). RCSC The Radio Components Standardization Committee (RCSC) is the body that originated the WG designations for standard rectangular waveguides. It also defined standard choke and cover flanges with identifiers of the form 5985-99-xxx-xxxx where the x'''s represent a catalogue number, not in itself containing any information about the flange. References Microwave technology