These curved flap discs were created specifically for finishing fillet welds and other hard-to-reach places. You can hit weld seams and slag with both the side and bottom of the flap discs. The zirconia grain is intended for use on steel and stainless. Its consumable fiberglass backing won't melt and smear or scratch the workpiece. This flap disc may be used as a conventional flap disc, and also for underhand applications using the top of the disc.