This Prime-Line N 7449 Bi-Fold Door Roller Assembly is constructed of a steel bracket and steel ball bearings with plastic rollers. It is commonly used on pocket door and by-pass sliding door systems. The bracket's mounting base measures 2-7/16 in. x 1 in. and it features 4-parallel wheels that are spaced apart at 7/8 in. on center. The wheels are constructed of durable plastic, which provide for a smooth, long-lasting, quiet operation, and they feature 7/8 in. Dia convex (round) edges. These adjustable roller assemblies mount on the tops of pocket doors and they are used by many pocket door manufacturers. This roller assembly fits into a 1-5/16 in.; wide track (inside dimension, wall-2-wall).