Abstract: An assembly kit comprising primary, secondary and intermediate sub-frames of tubular material which are all telescopically connectable to each other for erecting demountable frame structures.Each primary sub-frame has two side members and two cross members connected to the side members at positions spaced from the ends of the side members by a fixed distance. Two pairs of legs, having a length equal to the fixed distance, project respectively from the junctions of the side members and the cross members to one side of the side members.Each secondary sub-frame has two "L"-shaped side members and two cross members connected, respectively to the junctions of the arms of the "L"-shaped side members and at positions spaced by said fixed distance from the free ends the long arms of the "L"-shaped side members. The "L"-shaped side members are of tubular material which is a sliding fit on the tubular material of each primary sub-frame and have short arms equal in length to the fixed distance.