legs and tabs simply pressed into the desired configuration the height of the fastener member 10 is of such a dimension to fit closely within the channel member 4 and is capable of being spot welded therein the width of the fastener member 10 is of such a dimension that the open faced edge of the fastener member can bear against the internal surface of the channel member edges 6 and create an aperture on the fastener members other side adjacent the channel base 8 a guide sleeve 16 also having roughly a u shaped configuration is dimensioned to fit within the aperture created between the channel base 8 and the fastener 10 the guide sleeve 16 can be punched to relatively close tolerances from a sheet of plate metal and is of the same height as the fastener 10 the guide sleeve 16 thus removes any requirement of close tolerances for the frame channel member 4 the guide sleeve 16 like the fastener member 10 can be spot welded within the rigid channel member 4 referring specifically to fig2 a foot support member 18 having an upright male channel 20 is designed to be relatively movable within the female aperture defined by the guide sleeve 16 and the fastener 10 the upright channel 20 has relatively small edge extensions 22 that are approximately one ninth the width of the base portion of the upright channel the small edge extension 22 save in the use of metal compared to the prior foot supports while still providing both strength and guide surfaces the dimension of this upright channel 20 is such as to fit flush within the guide sleeve 16 as can be.