PFERD Standard twist knot cup brush with brass wire for use on large surfaces where a great deal of roughing is required. Good for corners and angles, and removal of contaminants such as scale, concrete, slag, and marine growth. Specification: Diameter (inches): 3-1/2; Thread Size: 5/8-11; Wire Size: .014; Trim Length (inches): 7/8; Maximum Rotational Speed (RPM): 12500.