These burs are made of state of the art metals for high speed use in removing metal for gemstone and diamond settings. They are used by jewelers like a dremmel or flex shaft rotary precision motor would be, but are customizable for each particular job. For bezel settings you might want to choose a round bur, and for undercutting prongs for a diamond setting, you may use a 45 degree or a 90 degree bur for a good fit. For other shapes like square and marquise settings, a combination of heart shaped and other burs are usually used. Jewelers burs are cutting tools that make your setting work easier, and they should be cared for to ensure maximum effectiveness. By using bur lubricant you will be able to extend the life of your burs.