This part of IEC 63171 describes shielded or unshielded circular connectors with 2 ways and M8 or M12 Styles, typically used for data transmission up to 600 MHz and with current carrying capacity up to 4 A, for use in areas with harsh environmental conditions. These connectors consist of fixed and free connectors either rewirable or non-rewirable. Male connectors have square cross- section contacts, for data and power transmission. M12 describes the dimensions of the styles and thread of the screw-locking mechanism according IEC 61076-2-101 of this size of circular connectors. M8 describes the dimensions of the styles and thread of the screw-locking mechanism according IEC 61076-2-104. The use of alternative locking mechanisms according to IEC 61076-2-010 or IEC 61076-2-011 are possible. The coding provided by this standard prevents the mating of accordingly coded male or female connectors to other similarly sized interfaces covered by this or other standards. These Type 5 connectors are interoperable with Type 2 connectors according IEC 63171-2, except the locking and sealing system provided by the outer shell. The shielded and unshielded connectors are interoperable for their internal transmission performance and can be exchanged. The shielded version has improved EMC and coupling properties. This part of IEC 63171 covers Type 5 connectors. Each part of this series has the associated type number equal to the number of the part in the series. All connectors in the IEC 63171 series are deemed to provide the same functions as defined in IEC 63171:2021, using different mechanical interfaces.