"RoyJ" wrote in message
...
I'll try a more basic answer: The old line chucks were screwed onto a
threaded spindle. These don't give a positive centering action as they
wear as well as a little problem with high speed reversing: If you
accidentally hit reverse, the chuck would unscrew and sail across the
room.

The D series have a short taper that centers the chuck, along with 3 pins
with cam holes to positively lock things into place. To pull a chuck off
you unlock the cams half way, pound on the chuck with a rubber hammer to
pop the taper, release the cams all the way to allow the chuck to come
off. Put the new chuck on the spindle, tighten the cams. The cams usually
use the same key as the chuck, are located in the collar.

Now I got it. Thanks.