3015-Crown drill bit arbor blade U drill violent drill small diameter shovel drill CNC high speed extended internal cooling deep hole drillHigh efficiency crown drill for deep hole processing: 1. The crown drill is a new generation of hole processing tools, with a more advanced drill body structure and blade design than the U drill. It is better than the U drill in terms of accuracy and finish, and integrates drilling and boring in one! 2. The whole is made of H13 high hardness steel, and the quenching and forging make the drill bit more durable. 3. Extraordinary penetration and