Flap discs are used in heavy stock removal, usually weld removal. They outperform Resin Fiber Discs due to their increased lifetime. Resin Fiber discs are only two dimensional, once the abrasive surface wears down the product is finished. To achieve a finish equivalent to a resin fiber disc always use a flap disc one grit coarser. E.g. if the operator is running a 60 grit resin fiber disc try a 40 or 50 grit flap disc. This is a mixed grit bundle with five pieces of each grit (40, 60, 80, 120).