If one were to search on Amazon for "Test Indicator Flexible Holders" you will turn up many items using this mechanism (please ignore the magnetic base; I'm not focusing on that part, just the red components and the knob):
You can watch this video to see how they work:
It is clear from that video that, indeed, that single knob tightens down both (ball?) joints, both the joint mounted to the top of the magnetic base, but also the joint closest to the holder that is intended to hold the oscilloscope probe.
My question is two-fold (primary/important question is first):
Exactly how does this entire mechanism act to clamp both arms rigidly, in space? From the video and the pictures, it is not readily apparently what clamping action is at play here. My only guess is that there is some clamping action acting upon both links, but how can the single big black knob act to clamp all (ball?) joints?
Does this entire mechanism have some "standard" name in the industry? I know about ball joints, but are these really just ball joints? I speculate that these aren't true ball joints, because of the single knob being sufficient to clamp them all rigidly, leading me to speculate that the combination of joints, linkage arms, and joints have some standard name.