This is a tension spring roller assembly with an offset tension spring design used by Academy and a variety of other patio door manufacturers. The roller is a 1 in. steel ball bearing roller attached to an offset heat treated tension spring. The 2-1/4 in. offset flat spring installs into the screen door frame and provides the tension required for the screen door to slide smoothly. For high density polyethylene ball bearing roller use Prime-Line part B 686. Color: Aluminum.