shown the tube forming frame members 101 and 12 block 120 has a threaded opening 121 adjacent one end and also a through hole 122 a cap screw 124 passes through an opening in tube 101 and is threaded into the opening 121 the cap screw securely clamps the members 120 to tube 101 a second member 125 also fits into the end portion of tube 101 and has a relief cut in one surface so the two members 120 and 125 are spaced slightly as shown at 126 the two parts 120 and 122 are inserted into the rear frame member 101 a cap screw 127 is passed through a provided opening in the lower wall of the frame member 101 through the opening 122 and is threaded into an opening 128 in member 126 the opposite ends of members 120 and 125 are slipped into the outer end of frame member 12 before cap screw 127 is tightened and frame members 101 and 12 are abutted then the cap screw 127 is tightened and it will spread the ends of members 120 and 125 which are inside tube 12 to securely hold the two frame parts aligned and in assembly the same type of fasteners are used for frame members 20 and 102 and cross bars 30 and.