The through connector (or adaptor) is mounted in a patch panel, of an optical fibre termination unit, or OFDF, and allows a pigtail to be connected to a patch cord. The pigtail is usually fusion spliced to an optical fibre of an external cable; and the patch cord connects to transmission equipment. A through connector allows the optical transmission system connection to be quickly made and broken, as required. This enables fault finding and maintenance activities (such as service restorations & re-arrangements) to be undertaken quickly and efficiently. Two way (Duplex) connectors/adaptors are described for a very small (eg mini) size LC connector. The adaptor unit comprises a plastic body, and inner part with a precision alignment mechanism; which is made to demanding specifications. The alignment sleeve and precision body ensures: reliable, long term, mechanical and optical performance for the through adaptor.