The Black RSC Soft Disk is used for sharpening delicate instruments and scissors. The soft rubber carbide finish sharpens the instrument without damaging the fine metal that is used to make the instrument valuable. This disk is used for micro scissors, fine bladed knives, biopsy punches, and delicate blades. Please Note: The RSC disk is available in two different shaft shapes, please look at the shafts on your machine to determine which one you will need. The "R" Shaft is perfectly round and the "D" shaft has a flat side to the shaft.