IEC 63138-2:2023 is available as IEC 63138-2:2023 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 63138-2:2023, which is a sectional specification (SS), provides information and rules for the preparation of detail specifications (DS) for MQ4 series circular connectors with four RF channels, as well as a detailed specification of the blank format. An MQ4 series circular connector with 50 Ω nominal impedance has four RF channels which can be engaged and disengaged at the same time. There are two versions of plug connectors, one is a quick-lock version, and the other is a threaded version. The socket connector provides two coupling mechanisms, a quick-lock and a threaded coupling. MQ4 series circular connectors can be used in mobile communication systems and in other communication equipment. This document also specifies the mating face dimensions and gauging information of MQ4 series circular connectors, and tests selected from IEC 63138-1, applicable to all detail specifications relating to MQ4 series circular connectors.