device is made hollow so as slidably to accommodate both the projection 41 and the mounting bracket 51 within its interior referring to fig3 and 4 which show the cross sectional relationship of parts adjacent to the inboard and outboard extremities of the convertible bed device respectively the preferred form of interengagement between parts will be described as shown in fig3 the interior of the standard 22 of the convertible bed device is formed with a narrow recess 70 into which the rectangular block 44 on the projection 41 is snuggly accommodated the block 44 is preferably enlarged slightly to provide localized contact between the parts although the recess 70 might be constricted to provide the same results at the lower edges the walls of the standard 22 are thickened inwardly as at 71 and 72 to provide localized contact with the front and rear surface 42 and 43 of the projection 41 since the points of localized contact between the standard 22 and the projection 41 are located adjacent to the fastening screw 50 about which all movement of the mounting bracket 51 occurs a minimum of interference will arise should the position of the mounting bracket have to be adjusted the three.