Wood Hub Wheel Brush, 3 Rows, Converging, Overall diameter 3"Wood Hub Wheel Brush, 4 Rows, Upright, Overall diameter 3" consists of Chungking bristles mounted into a hardwood hub with 1/4" arbor hole tapered to fit tapered spindles of polishing motors. Wooden Hub diameter is 1 5/8", Trim length is 11/16".Bristle tufts are "staple-set" into wood hubs to remain securely fastened.