Ive never seen one before either, but I would imagine it works like the bumper jacks from the late 60's and early 70s. It might have some sort of paw that locks into the threads after another paw raises it up. I can't see how there is enough mechanism there to make it thread up the ACME looking screw.
I'm thinking it works a ratcheting nut inside the housing but I haven't seen one of those for over 50 years. They aren't even close to being stable with a car jacked up with one.
Does it have a split nut that slides upward and then closes down on a thread with each ratchet the handle?
I'm gonna say that it's threaded only for speed adjusting to get it close then it works like any other jack. If you look close you will see that it has a buttress type thread which is flat on one side. This type of thread was used for extreme loads.
It is like the 60’s GM jacks that had teeth inside the column. It is just round instead of a rectangle. It is not threaded.
My guess is European. I don't remember the exact configuration, but my Spridgets had a reinforced hole in the rockers for a stub like the one sticking out on the side of the pictured piece. The stub was angled like that so that theoretically the jack wouldn't get into the paint.