A twist drill is an instrument that cuts a circular hole of a workpiece by rotating relative to a fixed axis. It is so named because its cheap flute is spiral and shaped like a twist.
The main cutting edge of the end mill is a cylindrical surface, and the cutting edge on the end face is a minor cutting edge. At work, an end mill without a center edge cannot go anywhere the axial direction of the milling cutter. According to the national standard: the end mill has a diameter of 2-50mm and can be divided into coarse and fine teeth. Diameters 2-20 are straight shank ranges and diameters 14-50 are tapered shank ranges.