IEC 60169-17 Amd.1 Ed. 1.0 b:1993

Amendment 1 - Radio-frequency connectors. Part 17: R.F. coaxial connectors with inner diameter of outer conductor 6.5 mm (0.256 in) with screw coupling - Characteristic impedance 50 ohms (Type TNC)

International Electrotechnical Commission , 04/26/1993