This is one of the more critical factors that determine an end mill’s performance. If the number of blades on an end mill is small, it would result in a small cross-sectional area and, thus, reduce stiffness, which may cause bending during cutting, but on the other hand there is a large space for discharge of chips, which makes the discharge convenient. If the number of blades is large, the chip pocket becomes small to allow a reduced capacity for chip storage but, conversely, its cross-sectional area as well as stiffness increase.