central portions 42 the web portions 45 terminate in connecting folded flanges 46 which extend outwardly substantially perpendicular to web portions 45 the above described face plates 41 are reversely positioned with central portions 42 thereof spaced apart and with connecting flanges 46 juxtaposed juxtaposed connecting flanges 46 are then secured together by vertical member 48 which extends substantially the height of the face plates 41 vertical member 48 is of heavier gauge sheet metal or may be an extrusion and has a central channel 49 which encloses connecting flanges 46 to hold them together the vertical member 48 is bent outwardly at the edges of the central channel to define web portions 50 which extend substantially perpendicular thereto when assembled the web portions 50 are adjacent to and extend substantially parallel to the web portions 45 of the face plates 41 the web portions 50 of the vertical members 48 terminate at outwardly bent edge flanges 52 the edge flanges 52 form j shape projections and include main portions 53 intermediate portions 54 and terminal portions 55 main portions 53 of the edge flanges 52 extend outwardly substantially perpendicular to web portions 50 intermediate portions 54 extend outwardly away from the main portions 53 terminal portions 55 extend inwardly from intermediate portions 54 thereby being inclined back toward the web portions 45 of the face plates the terminal portions 55 terminate at edges 58 which are spaced outwardly from the web portions to define recesses 59 longitudinally spaced slots 60 are formed in main portions 53 of the vertical member and are in the back of recesses 59 it should be appreciated that.