Features:Brand new and high quality. The ladder of its unique structure, a bit can open a variety of specifications of aperture. Do not need to use center punch, compared with the ordinary twist drill is not easy to be broken. Deburring, chamfering, elliptic hole enlargement, twist drill, the function of them was unable,but it is possible. The use of tools: drill, bench drill.Work while water cooling, can effectively extend the service life of drill bit, recommend drilling rate of 250-250 RPM.