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.

Michael Koblic wrote:
Looking at chucks from various sources they seem to be mounted on lathe
spindles in a variety of ways. Most of the time I can grasp what is going on
but some of the designations stumped me: What is the D 1-4, D1-6 etc.,
mount? Books and Google are no help.

Thanks,