4″ Crimped Wire Cup Brush- Carbon Steel. For lighter duty surface cleaning a Crimped style Cup Brush is appropriate. Crimped wire is less rigid than Knotted and can get into crevices more easily. Milwaukee offers a full range of Crimp and Knotted Wire Cup Brushes. This Crimp Wire Cup Brush is designed to be used on 7 inch Milwaukee and competitive Grinders with 5/8-11″ threaded spindles. Made from carbon steel wire.