IEC 60169-21 Amd.1 Ed. 1.0 b:1996

Amendment 1 – Radio-frequency connectors. Part 21: Two types of radio-frequency connectors with inner diameter of outer conductor 9.5 mm (0.374 in) with different versions of screw coupling – Characteristic impedance 50 ohms (Types SC-A and SC-B)
Amendment by International Electrotechnical Commission, 01/23/1996