IEC 61753-052-6:2016 contains the minimum initial test and measurement requirements and severities which a fibre optic attenuator satisfies in order to be categorised as meeting the requirements of single-mode fibre non-connectorized fixed attenuator devices used in outside plant environments. IEC 60869-1 contains the generic specification of the optical attenuator. Optical performances specified in this document relate only to non-connectorized optical attenuators. Keywords: non-connectorized fixed attenuator devices, Category O in outside plant environments