A telescopic beam has a cross-section comprising an array of members (11-17) whose cross-section are of essentially spiral or modified spiral form such that members have lengths of identical (or broadly identical) cross-section (in profile and dimension) and constant (or broadly constant) cross-section along their axis. In the array the members are rotationally offset relative to one another about an axis (A) of the beam parallel to their own axis. In addition the members in the array engage one another such that relative linear movement between two adjacent members is constrained to be possible only in the direction of their axis. The array is assembled to produce the telescopic beam. The maximum number of members in any beam is dependent on the magnitude of the rotational offset incorporated in the particular section used. Any amount of rotational offset can be selected and so can any number of sections from a minimum of two to a maximum restricted only by the practical limits of the production process and the material chosen.