On Fri, 1 Jan 2021 23:01:02 +0000, Bob Massie
wrote:

Hi, I have acquired a 10" 9-R columbian wood vice. It slides back and forth freely. Fliped it over, removed 2 lg screws, removed cap and nothing there to move jaws when handle turned. Where might I find this part that goes on the center threaded rod ??? please help

Here's a thread from someone else with the same vise and missing part.
https://www.lumberjocks.com/topics/52709
Here's a discussion that was cited in that thread:
http://zengrain.com/desmond-stephan-and-morgan-vise-half-nuts/

I don't know how helpful they are but Milwaukee Tool & Equipment
apparently has a half-nut that can be adusted to fit without much
effort.
http://www.milwtool.com/v_wood.htm

Other options get more difficult:

You can get regular steel nuts with Acme threads from McMaster for not
a lot of money, but they won't function in a vise without some work
being done on them. This might be as little as grinding to fit or may
require some welding.

Failing that you'll likely have to make a part or have one
made--doesn't take a lot of lathe to do it--a Harbor Freight 7x10 will
do it but by the time you've bought the lathe and associated tools
you've paid for several good new vises.