This is an extra heavy duty plain back, tandem roller assembly used by Kawneer on their heavy doors. Often found in Hawaii used on door walls, it has an in-line tandem inner housing with 1-1/2 in. concave or grooved steel ball bearing rollers set in a heavy duty diecast outer housing with rear adjustment. The housing is 1-13/16 in. tall and 1-1/8 in. wide and is held in place by screws from the top as well as the end.