In my head I have a kind of picture how a rotary table might be made.

You have a base, with a central pivot (could be bored for a taper). Around
the pivot is a gear & the table, driven by a worm.

Some of these tables are advertised to have a method by which the table can
be decoupled from the gear, to allow quick rotation without turning the
worm. I have been turning this picture around and around in my head and
cannot figure out how they do this.

Someone tell me or point to a drawing, please...