The files attached are of the top of the drawbar from an Index Model 40 milling machine.
This style of drawbar is captured by the black nut on the top of the spindle.  When loosining the drawbar the collet is forced from the spindle by the collar on the drawbar rising and hitting the top nut.  Picture 1 shows the drawbar, brass bearing, and the top nut on the bench.  Picture 2 shows the top of the spindle without the drawbaR.  pICTURE 3 IS AN EXPLODED (?) VIEW OF THE SYSTEM, AND PICTURE 4 IS HOW IT LOOKS ASSEMBLED.