This is a "B" tab patio door roller assembly with a 1-1/4 in. concave or grooved plastic ball bearing roller. The housing is 11/16 in. wide and 1-7/16 in. tall with a rear adjusting screw. The "B" tab secures the assembly as the mounting screw is driven up through the "B" tab hole and into the door's bottom rail mounting hole. Used by a variety of sliding patio door manufacturers.