This is a tension spring roller assembly with a V-spring design used by Academy and a variety of other sliding patio door manufacturers. The roller is a 1 in. high-density polyethylene 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.