This standard describes circular M12 connectors typically used for industrial process measurement and control. These connectors consist of fixed and free connectors with screwlocking as well as adaptors. The connectors are suitable to connect two optic fibres and two electrical wires intended for power transmission to the optionally integrated transmitter and receiver, not specified in this standard. Male connectors have round electrical contacts Ø 1,0 mm and round optical contacts with the ferrule Ø 1,25 mm according to IEC 61754-20, grade 1 for All-silica optical fibre cables single mode fibre 9/125 μm multimode fibre 50/125 μm or 62,5/125 μm NOTE M12 is the dimension of the thread of the screw locking mechanism of these circular connectors. Throughout this standard dimensions are in mm.