Imagine have a cocker ram hooked up with long low pressure hoses and unscrewed from the body. You grab the threads of the ram shaft, and then start pulling the trigger. The shaft will not move, but the entire ram moves on the shaft. That is basically how the ram-bolt works.
The thumb screw enters the top of the body holding the brass center ring (which represents what would be the head of the ram shaft) stationary so the bolt will move (like the ram body in the above description).
The lp hoses enters the upper tube of the body by way of the barbs you see on the side. Pretty much making the top tube of the marker a ram.....