width of the openings next each section is inserted in the hollow space 11 between the openings 8 and 10 the flanges 51 and 52 of each section are disposed between the front skin 7 and the back skin 9 and extend away from the opening 5 welds 13 are placed in the weld pockets 57 to secure the channel sections to the front door skin 7 and back door skin 9 next the first frame sections 19a b c d are cut into four sections according to the height and width of the openings 8 and 10 and mitered at the ends as shown in fig9 generally the first frame sections 19a b c d are inserted around the front opening 8 preferably the two sections of first frame 19 that form the vertical components and are cut shorter than the height of the front opening 8 the horizontal components of first frame 19 are cut longer than the width of the front opening 8 referring to fig1 the horizontal sections are installed first the ends of the horizontal sections slip behind the front door skin 7 and contact the interior surface 90 referring to fig1 the vertical sections are installed next the ends of the vertical sections do not slip behind the front door skin 7 since the sections are shorter than the height of the front opening 8 however the ends of the vertical sections extend over the horizontal sections to provide a mitered appearance at the corners each section of the first frame 19 is attached to the channel 17 by inserting the self tapping screws 29 through the openings 27 and threading the screws 29 through the guide groove 25 of the channel.