Defines the standard interface dimensions for the type FC-PC family of connectors. The parent connector for type FC connector family is a single position plug connector set of plug/adapter configuration which is characterised by a 2,5 mm nominal ferrule diameter. It includes a thread coupling mechanism, which is spring loaded relative to the ferrule in the direction of the optical axis. The plug has a single male key which may be used to orient and limit the relative position between the connector and the component to which is mated. The optical alignment mechanism of the connectors is of a rigid bore sleeve or a resilient sleeve style. "