ATOPLEE 3/16-7/8 inch 1/4-1-3/8 inch HSS Cobalt Large Step Drill Bit Universal 10mm Round Shank Multiple Hole, 2 pieces Material:HSS4241(Suit for use in hardness under 25 ) Surface treatment: Titanize Shank diameter 10mm size: 3/16-7/8" & 1/4-1-3/8'' You can use water to cooling it when it is work and it can be used for even longer