This is an adjustable mirrored door assembly with a 1-1/2 in. concave nylon roller and used on Cox Series 21 and 22 door systems. The unique design has bottom feet, or brackets, that fit under the door frame and are fastened into place there then up the side. The 1/1-2 in. nylon roller provides a smooth ride for heavy mirrored doors. May need to adjust if you notice any binding.