Probably the toughest brushes in the world and they need to be, bearing in mind the work they are called on to do. Used for heavy duty cleaning operations, de-rusting, cleaning welds, etc. Offered in two forms, either crimp wire or heavier duty twist knot. A word of caution - before ordering check your grinder's speed. The greater the brush diameter the lower the maximum permitted safe speed. The maximum RPM for the 65mm diameter is 12,500rpm, 70mm is 11,000rpm and the 80mm is 8,500rpm.