Martin chain tighteners are economical to use. They provide everything needed for a quick, easy installation. There is no need to design, procure or custom make and assemble separate parts. They accommodate mounting in several different positions, parallel or at 90 deg to the mounting surface and as a cantilever or attached each end. Martin Chain Tightener, Single Adjusting, For Use With: Idler Sprocket, 5/16 in Stud Hole, Steel, 6 in L x 1-1/8 in W