This is a U-back patio door roller assembly with a 1-1/2 in. concave (center grooved) steel ball-bearing roller. When installed the U-back housing is drawn tightly into position against the side stile as the mounting screw is tightened. The housing is 25/32 in. wide, 1-7/16 in. tall with a rear adjusting screw. Used by Crown manufacturing, Pennco, and a variety of other patio door manufacturers.