Features:Brand new and high quality. Type: 3-13MM (11 steps:3, 4,5,6,7,8,9,10,11,12,13MM). 4241 high-speed steel, used in hardness under 25 Â° workpiece, the plate thickness under 5 mm. such as carbon steel plate, sheet iron, insulation boards, wood. Cannot be used for stainless steel. When inject cold water while working, can effectively extend the service life of the drill bit.