This is an "F" tab patio door roller assembly with a 1-1/4 in. concave steel ball bearing roller. When the corner screw passes through the "F" tab the assembly is captured by the side stile and bottom rail as the screw draws the two sides together. The housing is 3/4 in. wide and 1-1/8 in. tall with a rear adjusting screw. Used by Christian Porter, Fullview and a variety of other patio door manufacturers.