This Prime-Line N 7410 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 inch; x 1 inch; and it features 4 parallel wheels that are spaced apart at 1-3/16 inch; on center; The wheels are constructed of durable plastic, which provide for a smooth, long-lasting, quiet operation, and they feature 1 in; diameter 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 inch; wide track (inside dimension, wall-2-wall).