This is a Medium Ball Nose - Foredom Ceramcut Blue Stone with a 3/32" shank, 3/16" head diameter and grit 120 (Fine).
These stones leave a relatively fine finish making them suitable for detailing and texturing work. They would typically follow the use of the V stones with their finer grit and smaller heads. The ceramic and aluminum oxide abrasive grain structure is superior in performance and life to standard aluminum oxides or silicon carbides. Widely used on hard metals, including hardened and mild steel, steel alloys, chrome cobalt, titanium, platinum and other ferrous metals. Also suitable for porcelain materials and wood. CeramCut Blue Stones remove material faster, run cooler, and last 3-5 times longer than other abrasives. Non-impregnating and non-contaminating. 45,000 RPM Max Speed. Made in USA.