Knot Cup Brushes are for heavy-duty use for the preparing of metal surfaces before painting, & the removal of slag, rust, scale or concrete waste. Lessmann knotted brushes are filled with a special steel wire of high tensile strength in order to meet the demands of this type of brush. Diameter: 65 mm. Bore. M10. Wire Gauge. 0.50. Wire Type: Steel. Max. R.P.M. 12, 500.