that is used with screening of enclosures which is not a part of the subject invention and is therefore not illustrated beam half section 46 has flanges 58 60 generally parallel to one another two u shaped receptacles 66 68 face one another with prongs 70 72 having triangular shapes and located in the inside corners of the beam half section 46 adjacent the flanges 58 60 a nesting receptacle 74 and inner lip 76 are formed adjacent the inner corner where flange 58 meets the main section of beam half section 46 likewise beam half section 48 has flanges 78 80 generally parallel to one another a nesting receptacle 86 and lip 88 is formed adjacent the inner corner of where flange 80 meets the main section of beam half 48 in accordance with an example embodiment of the invention to fully rigidify the lapped and locked flanges of the beam half sections a second nesting receptacle and lip is formed for engaging and holding the free end of the respectively outer flange of the beam half sections thus as illustrated in fig5 a nesting receptacle 90 and lip 92 are defined to receive and hold the free end edge of flange 58 and a nesting receptacle 94 and lip 96 are defined for engaging the free edge of flange 80 thus the free end edges of each of the flanges of the respective beam half sections are received.