Abstract: A two-part optical fibre adapter means suitable for coupling optical signals in electronic shelf assemblies incorporating plug-in circuit boards for high density racked optical systems. One part of the adapter means is mounted in an aperture in a support member and has a thread which is provided for attachment of an optical-fibre connector. The other part incorporates a light-emitting diode and is resiliently mounted by means of a helical spring in an aperture in a further support member. The other part which takes the form of a spigot slidably locates in a bore of the one part and cooperates with a pin of the optical fibre connector which is attached to the one part. A plurality of the optical-fibre adapter means are mounted on an equipment shelf back-plane and a printed circuit board. Use of adapter means of this type eliminates the requirement for inter-link cables between the back-plane and the p.c.b. which have been required hitherto in such equipment-shelf assemblies.