This is a Mono-rail roller for drawer slide systems. Roller mounts on left hand side of drawer as viewed from the rear; 13/16 in. outside diameter of the nylon roller. With the 13/16 in. diameter roller features a 3-1/2 in. high bracket. Roller is a 5/16 in. in width. It mounts on the left side of your drawer when viewed from the rear. Contains 2 rollers and includes fasteners for a quick and easy installation.