Two flat edge nylon wheels come fixed in an offset adjustable bracket. This bracket easily mounts to the top of your door. Fits a 3/4 In. to 1-3/8 In. thick Harvey or similar styled door. top, center mounted, adjustable, tandem roller assembly. The 1 inch convex or round edged nylon rollers are attached to a stamped steel tandem housing mounted on top of a 5/16 inch threaded steel rod.