This document covers shielded or unshielded free and fixed connectors, circular or rectangular, for balanced single-pair data transmission, with current-carrying capacity.

It also covers the portion for balanced single-pair data transmission of combined, shielded or unshielded, free and fixed connectors, circular or rectangular, having additional contacts for power transmission, whose performance requirements are described in a product detail specification, see Annex A, of the IEC 63171‑X series, (type X connectors), or in a separate document, either an IEC product detail specification, see Annex A, or manufacturer's specification.

This document does not describe a specific mating interface. It specifies the IEC 63171 series - or other documents referencing it - common mechanical, electrical and transmission characteristics and environmental requirements, as well as required test specifications.

Within their own type, the shielded and unshielded connectors are interoperable for their transmission performance and can be exchanged, although the shielded version has improved alien crosstalk and coupling attenuation properties.

Single-pair connectors of this series can be grouped to one body of multipole connectors or combined with other connectors, e.g., power connectors, also known as combined (data or signal, and power) connectors.