Yeah, we are a little confused. Most of us are talking about the long threaded screw that moves the whole plate up and down.
What "little" travel are you talking about?
Those knurled nuts that you showed us are just to provide an easy way to join the long threaded screw to the pivot. They are not fine adjustment nuts on the screw. They are just to keep the long screw from falling out and have something to push against.
It's just to provide easy assembly and tear down for travel, without the need for tools. Don't over think it.
Once you have the plate adjusted for your latitude, you tighten everything down and never adjust it again, until you travel to another latitude location.
There should be a set screw or grub screw that holds it to the longer threaded screw so it stays in one position as the Jack screw turns. If it stays in one place (on the jack screw and does not turn along with tee jack screw) and starts to back off, you don't have the set screw tight enough on the longer jack screw.
I think this is where your problem lies. look closer at the knurled thumb nuts around the outside.
In your picture I think I see a slotted set screw. Tighten that down.
The reason for the jack screw is to adjust your mount with the full weight of the telescope and gear on it if you have to make fine adjustment in the field when lining up the north polar position.
It's a convenience device.
Edited by GalaxyPiper, Yesterday, 10:44 AM.