are bent perpendicular to the face of the panel in the same direction additionally tab 3 r and tab 3 l are bent all in the same direction as the top and bottom rails and are perpendicular to the face 7 finally the top rim 5 t and bottom rim 5 b are bent perpendicular to the top 1 and bottom 2 rails towards each other fig5 is of a rectangular shape panel fig5 is rigidly fastened in to shape by joining the 45 u00b0 degree cuts 46 on the side 3 r top and bottom and tabs 3 l top and bottom this is done by placing the locking plate 42 on the inside of tab 3 l and 3 r straddling the seam line 48 and rigidly affixing the locking plate 42 to the inside of the tab 3 r and 3 l by the use of locking rivets 44 in other words the rivet inserts through the outside of the steel into the locking plate fig4 is a magnified view of the vent 12 detail the vent 12 is directly machined into the panel leaving the surface smooth the diameter of the vent holes 12 a is determined by the required airflow specification the vent 12 is machined into the panel in a lateral plane commencing at a minimal one inch below the top rail 1 running.