A feature of a connector system that prevents physical mating where the service or orientation is incorrect. For example, keyed jacks may be used on all data connections to prevent plugging them into the phone system. Some networks, such as FDDI, have distinct keying guidelines and requirements.
A mechanical arrangement of guide pins, guide sockets, keying plugs, contacts, bosses, slots, keyways, inserts, or grooves in a housing, shell, or insert that allows connectors of the same size and type to be lined up side by side with no danger of making a wrong connection. Keying may also be accomplished by numbering the connectors and matching panel positions, or by using connectors of a different size or color. Under certain circumstances, keying and polarization may be combined in a connector design.