Mechanical watch parts of the larger force is up and down the axis of the shaft and the center shaft up and down the hole, so the two parts shaft hole wear is relatively large. However, due to the location of the large steel wheels, making the two holes wear different orientation. Mechanical parts in the mechanical watch is the shaft up and down the hole and the two axle (center axle) up and down hole, and therefore shaft wear is relatively large, especially early watches to reduce costs, most of the movement is 15 drill or 17 Drill, often not installed in these two parts of the drill. Watch a few years later