Spindle lock is a function that allows you to mechanically lock the rotation of the milling machine spindle. The spindle is the main shaft of the machine into which a work tool, such as a milling bit, is clamped. When changing this tool, the clamping nut must be loosened or tightened. Without the lock, the spindle would rotate freely during this operation, requiring the use of two wrenches - one to hold the shaft and one to turn the nut. The lock, which is usually activated by pressing a button, locks the spindle in one position. This allows convenient and quick tool changes using only one wrench.