A fitting is provided for use in retaining a plurality of accessory members to a vertical modular structural unit of a telecommunications tower or electricity pylon. The unit has a plurality of vertical sides wherein each side has at least one side aperture. The fitting has a body; a body plate attached to the body and so-shaped as to be cooperable with a side of the unit and receivable in intimate engagement within the side aperture; attachments by which the fitting is attachable to the structure and the body plate is retained thereto receivable within the side aperture by retaining bolts; the body having at least one accessory, such as a guy rope, insulator, dish and platform-receiving aperture for retaining the accessory to the body. The shape of the apertures in each unit side which is complimentary with the body plate, provides a lighter, stronger and more efficacious modular unit and tower.