Flap discs are used in heavy stock removal, often weld removal. They outperform Resin Fiber Discs due to their increased lifetime and last twice as long as Aluminum Oxide discs. 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 grit flap disc.