Abstract: A frameless truck cap lift door is disclosed having a concealed hinge structure and including a transparent window portion of generally uniform thickness having six holes, two of which extend along an upper edge thereof. There is a relatively rigid support bar having at least a pair of holes which are simutaneously alignable with the window holes. A pair of hinges are adapted to be fastened near an upper edge of the truck cap each hinge having a pivotable arm extending from the truck cap and terminating in an apertured flange. The spacing between the flanges when the hinges are fastened to the truck cap is substantially the same of the spacing between the holes in the support bar and the holes in the window whereby a pair of threaded fasteners may be passed each through the window, the support bar and one flange for securing the window pivotably to the cap.