Used by Northrup and a variety of sliding patio door manufacturers 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 1-1/4 inch diameter concave ball bearing roller Stamped steel housing and steel rollers Used on metal framed sliding patio doors Easy to install A Phillips head screwdriver is required for installation Please refer to the line art drawing for dimensions and compare with your needs before ordering