This is Dremel's 25/32" Silicone Carbide Grinding Stone Accessory Bit.
A high-quality industrial abrasive made for extended usage.
Ideal for sharpening, deburring, cleaning and general purpose grinding on harder materials--including stone, glass, ceramic, porcelain, gemstones, and nonferrous metals.
Specially designed for working with flat and slotted surfaces.
Use for all types of deburring, blending and finishing operations.