required other arrangements may also work such as providing a block on either side of the pivoting bracket 10 with a hole extending therethrough which registers with the sleeve 36 the retainer such as bracket s 100 includes a pair of end members 102 secured to the channel 80 and generally perpendicular to a bottom 81 of the channel 80 between which is disposed a pivoting bracket 10 a pin 104 is insertable through the end members 102 and the sleeve 36 in the base 12 of the pivoting bracket 10 to retain the pivoting bracket 10 in the channel 80 yet permit it to rotate about the axis 84 of the channel 80 preferably the bracket s 100 should be disposed in the channel 80 which is to say that the bracket s 100 should not project out of the channel 80 so as to allow the bracket s 100 to be installed when the panels are manufactured and the panels stacked without risk of scratching by the bracket s 100 of adjacent panels in the stack the door panels 50 52 and 54 may be constructed from a variety of materials for example as illustrated sheet metal may be used the panels 50 52 and 54 may be filled with an insulating material such as a urethane foam when uninsulated sheet metal panels are used it is preferable to include a reinforcing brace such as illustrated at reference 112 extending between the rear face 82 and a front face 88.