FavoriteUSA miniature mandrel-mounted end brushes are available in a wide variety of sizes. Excellent quality assures perfect smooth finish and long reliable use. One-piece ferrule construction insures that the stem and ferrule will not become separated during use. Maximum operating speed: 25,000 RPM. Hard Black Chungking Bristles Ferrule: 3/16" Trim 3/8" Shank: 3/32" (2.35 mm) Sold in packages of 12.