CNBTR 1mm Lapidary Diamond Coated Engraving Hole Saw Jewelry Beach Sea Shells Drill Bit with 2.35mm Dia Shank Pack of 20 Set of 20 pcs. 1mm Diamond Drill Bits - 2.35mm Shank Diameter Suitable for Jade agate, jade pearl shells, and carved grinding head holing needle bit crystal lettering Corundum tools by grinding machining, and drill slowly., or flour is not easy to rule out, tools (especially the small tools) is also easy to damage Please add water for coolant before you use Note:there are permissible variation in dimension.