surface 17 of rectangular recess 10 suitable fasteners 18 will connect l bracket 16 to the top of panels 12 and 13 likewise a plurality of fasteners 19 will secure the top portion of l bracket 16 to the overhanging recessed portion 17 of rectangular recess opening 10 if the building is constructed of cement block or other rigid material suitable cement screws 19 would be used to bolt l bracket 16 to the building structure in a similar manner elongated l bracket 20 is secured by means of fasteners 21 to the bottom edge of panels 12 and 13 the other portion 22 of l bracket 20 bent at 90 u00b0 will be secured to sill 23 of recess 10 by means of suitable fasteners 24 along the left and right hand vertical side surfaces of recess opening 10 are also provided l brackets 25 and 26 which are fastened to the vertical periphery of panels 12 and 13 by means of fasteners or screws 27 and 28 likewise the other portion of l brackets 25 and 26 bent at 90 u00b0 which abut the jamb or sidewalls of the recess 30 and 31 are fastened or screwed by means of suitable fasteners 32 and 33 to the building jamb surface if two flat panels 12 and 13 are used they can be easily installed after the.