Abstract: A hollow columnar structure fabricated from at least two, part-oval, extruded aluminium sections and intended for use as a sailing vessel mast or boom, a lamp standard or as piping. The sections each have a longitudinally extending groove along each of the longitudinal edges thereof, the grooves of one section being contiguous with the grooves of another when the sections are placed in position to form the columnar structure. Each groove is T-shaped in section whereby, when two such grooves come into co-operating relationship, the resultant cavity is of H-section. An H-shaped extrusion of synthetic plastics material is then inserted in each of the cavities to join the sections. The extrusions can be drawn through the cavities or can be extruded directly into the cavities. In an alternative form the structure is solid.