UNE-HD 351-4 S2
RIGID PRECISION COAXIAL LINES AND THEIR ASSOCIATED PRECISION CONNECTORS. PART 4:21 MM RIGID PRECISION COAXIAL LINE AND ASSOCIATED HERMAPHRODITIC PRECISION COAXIAL CONNECTOR. CHARACTERISTIC IMPEDANCE 50 OHMS (TYPE 9/21). CHARACTERISTIC IMPEDANCE 75 OHMS (TYPE 6/21). (Endorsed by AENOR in May of 1995.)