Abstract: An assembly jig, and method for assembling a clip-on eyeglass accessory, such as clip-on sunglasses, which is custom-made for a pair of eyeglasses, such as prescription eyeglasses. The accessory is made from two lenses, a lower clasp attached to the edge of each lens, and a unitary upper bridge piece which further includes an elastic bridge with an upper clasp on either end. The clasps are hook-shaped to hold onto eyeglasses by the spring force of the bridge. No accessory frame is needed because the four clasps attach directly to the lens. To assemble the accessory with the bridge and lower clasps in the correct assembly positions the jig makes use of lens holders. These lens holders are the same as those on which the accessory lenses have already been shaped in outline so as to match the outline of the eyeglasses. The lens holders are mated with respective lens mounts on the jig, and the jig permits adjustment of the distance between the mounts and the angles of the mounts.