Arbor hole-mount discs have a center hole to mount to an angle grinder arbor. Flap discs have flexible, overlapping flaps to blend, clean, debur, and finish metal. They are less aggressive at material removal than fiber discs and provide a more consistent finish than fiber discs and generally have a longer lifespan. Fiber discs attach to a backing pad and provide a balance of aggressive material removal and finish. Arbor-hole mount surface-conditioning discs remove rust, paint, and mill scale while creating a smooth surface for finishing.