Now the numerical control milling machining center more and more enters in the machine-finishing profession the Large and middle scale Enterprises, uses in complex work piece which processes the ordinary engine bed to process with difficulty. Must want to use the machining center to process the high accuracy the complex work piece, whether uses the end mill is a very essential aspect correctly. My factory use machining center had many years, I on many year use's in experiences discussed that uses several questions which the end mill should pay attention. 1 end mill loads when the knife holder the machining center clamps the way with end mill's attire, installs most with the spring clamp cover clamps. In milling processing process, if sometimes will not pay attention possibly will present the end mill to elongate gradually from the knife holder, will fall completely, cause work piece abandonment.