The Depth stop is mounted in the spindle and serves as a stop for the workpiece while using the 3 jaw or 4 jaw chuck. By using the Depth stop you are able to control the depth at which the workpiece is always stopped at. This allows you to chuck up numerous parts while maintaining the same machined depth each time. The stop can be adjusted by loosening the nut in the back and screwing the rod in or out and then tightening the nut again. The 30-degree collet like piece that fits in the spindle is threaded so that the stop rod can be adjusted for the desired depth.