This is a tension spring roller assembly, with a downward offset tension spring used by Academy and a variety of other sliding patio door manufacturers. The roller is a 1 in. high-density polyethylene ball bearing roller with a 1-3/4 in. long tension spring that is a heat treated steel spring. When installed the bent or angled, flat spring positions the roller assembly so that an adjusting screw adjusts the height of the roller as needed. For stainless steel roller assembly use Prime-Line part B 756.