Rex the Wrench wrote in
:

With the top nut installed on the spindle, loosening the drawbar
causes the shoulder on the drawbar to come up hard against the nut
which forces the collet or tool holder to unseat from the spindle. My
#645 Index (#9 B&S taper) and my Bridgeport "M" head (#7 B&S taper)
are both set up in a similar fashion.

Rex the Wrench

Rex, is the drawbar something more than a common drawbar?
Must be?