Well, I finally got my pair of spanner wrenches (bought from Micro-Tools Germany)...
I had to pay more taxes and dues than what I paid to Micro-Tools for the set, but that's another story
Anyway, I was finally able to adjust my Jupiter 12 in Kiev/Contax mount.
It was mis-focusing - focus on photos was closer than "aimed". It's a nice lens, good contrast, and I swore I'd try to fix the problem.
With the aid of those spanners, I did some adjustment, but was nonetheless forced to use thin paper shims on the back element.
It has a large protruding back element, which simply unscrews (at least in the Kiev mount version). With the aid of some "ground glass" (actually a piece of clear plastic with some frosted tape on the side facing the lens) and a handy loupe-microscope gadget, I was able to get the RF and the actual picture on the ground glass to agree after adding a thin paper "ring", so that the back element doesn't screw in all the way.
I used clear plastic + frosted tape because the real ground glass was too coarse.
Anyway, here's the photo of spanners and the lens.
Now I'll be able to work on the lenses, too, without fear of scratches, slippings, etc...
The spanners look and feel OK - it was the cheaper "economy" set, one with slotted and one with pointed tips.