The centering pin is a tool used to precisely align, or center, the milling machine base plate to the center of the motor. This alignment is crucial when working with accessories such as so-called "copy rings". A copy ring is an attachment mounted on the base that guides the milling machine along the edge of the template, thus allowing precise copying of shapes. If the base with the ring were not perfectly centered, the distance between the cutter edge and the guide ring would not be the same all the way around, resulting in an inaccurate result. The pin itself is clamped in the collet, the place intended for the cutter, and its tapered shape ensures that the base plate sits exactly in the centre position when the screws are tightened. Once tightened, the pin is removed and replaced with the work tool.