Professional kit: There are 20 different shapes and sizes of rotary knives, you can choose different types of cutter heads according to your work needs, to meet your different craft creation needs. > Multi-purpose: The diamond drill bit has 10 different grinding heads, which can be used for abrasion, engraving, cutting, polishing and engraving. Compatibility: 1/8' (3.1mm) handle, 39mm length, fits power rotary tools and most mini grinders. Very easy to use with a user-friendly design and simple insertion process. High quality material: The countersink drill bit is made of high quality high speed steel, which has a long service life and has the advantages of high hardness, good wear resistance , good heat resistance and good toughness. Shaft Diameter (3.1mm) Total Length (40mm) Package Contents: 20 X rotary files 1. When using a drill, the material temperature will be very high, please add water or coolant to avoid burns. 2. In order to better protect the tools, it is very suitable for wood, plastic and not too hard materials, it is best not to apply it to stone or other hard materials, which may shorten the service life . Good quality product