This part of IEC 61076-2 describes the B12 bayonet coupling interface of circular connectors employing the mating interfaces described in IEC 61076-2-101:2012 and IEC 61076-2-109:2014, that are typically used for industrial process measurement and control. These connectors consist of fixed and free connectors either rewirable or non-rewirable, with bayonet-coupling. These connectors may have glass to metal seal inserts. They have male or female contacts and are deemed be intermateable with corresponding free connectors produced according to this document. Male connectors have round contacts Ø 0,6 mm, Ø 0,76 mm, Ø 0,8 mm and Ø 1,0 mm. Differing codings prevent the mating of these individually coded fixed connectors (and consequently of individually coded free connectors deemed to bayonet couple with them) to other interfaces and cross- mating between the different codings. However, the styles and interface dimensions, except for the coupling mechanism, are given in 4.3 of IEC 61076-2- 101:2012 and 4.3.1 of IEC 61076-2-109:2014. The male type B12 circular connectors are interoperable with the female type B12 connector of the same coding and ways. The female type B12 connectors are interoperable with the male type B12 and M12 (threaded screw coupling) connector of the same coding and ways. NOTE B12 relates to a bayonet coupling with tube dimensions compatible with a M12 thread. M12 is the dimension of the thread of the screw-coupling mechanism of circular connectors covered by IEC 61076-2-101:2012 and IEC 61076-2-109:2014, which provide the mating interface (connector insert level) to these connectors with bayonet coupling.