Professional Kit: There are 20 different shapes and sizes of rotary cutters, you can choose different types of cutter heads according to work needs, they will satisfy your different craft creation needs. Multi-multi-function: Diamond drill bits have 10 different grinding bits for abrasion, carving, cutting, polishing and engraving. Compatibility: 1/8" (3.1mm) shank, 39mm length, fit for dremel electric rotary tool and most mini grinder. User-friendly design and easy insertion process, incredibly easy to use. Quality Material: The countersink bits is made of quality high speed steel with long life, has the advantages of high hardness, good wear resistance and heat resistance. Shank diameter: 1/8" (3.1mm) Total Length: 3/4" (40mm) Box Contents: 20 X Rotary Burrs 1.When using drill bits, material temperature will be very high, please add water or coolant to avoid being burned.< /p> 2.For better tool protection, perfect for wood, plastic and materials has not so high hardness, it's better not to apply to stone or other hard material which can reduce the period of use. Note: The data is manual measurement, please allow 1-21cm error, due to differences in light and screen, there will be a certain color difference, the specific received in kind prevail.