These are supplied with a 3mm integral arbor so that may be used in reversible drive drills and hobby drills like Dremel , Proxxon , Minitool & Minicraft etc. The shapes are turned down from steel before the grit is welded to the surface. This means that they are well balanced and run smoothly. They cut a wide range of materials in any direction with little need for finishing. Then shapes are available in coarse & fine and with certain shapes available in fine.