This is a steel tandem "C" tab roller assembly with 1-1/8 in. steel ball bearing rollers. The "C" tab fits around the corner screw and captured by the side stile and bottom rail as they are drawn together. The adjustable stamped steel housing is 11/16 in. wide with a flare width of 13/16 in., 1-1/16 in. tall and 3-1/8 in. long. Used by Pacific, Elco and a variety of other sliding patio door manufacturers.