This is a tension spring roller assembly with an offset or bent spring design used by Academy, Metal Industries and a variety of other patio door manufacturers. The roller is a 1 in. high density polyethylene roller with a tension spring that is a heat treated steel spring. The bent or angled flat spring installs into the screen door frame so that the roller assembly cushions the door as it rides back and forth. For ball bearing rollers use Prime-Line parts B 686 & B 576.