This part of IEC 61300 applies where optical fibre connectors are in practical use and it is necessary to ensure a designed minimum loss of the connector at a mating point. It aims at screening single mode physical contact (PC) optical fibre connectors of an optical patch cord and an optical pigtail cord in terms of return loss, thus ensuring minimum return loss when the connectors, which have been screen tested by this method, are randomly concatenated each other in the fields.