I have this small clamp - its about 2" / 5 cm tall:
I'm not sure where it came from so I don't know what its for. Note the pin on the right side which is removable - I assume this is to allow something to fit in the clamp from the side?
I suppose it could be more of a press than a clamp but I don't think you could get much pressure given the small size of the main knob.
Searching for terms like "castaloy small clamp" returns lots of hits but nothing that seems to match this particular tool.
Fine-machined adjustment screw for very accurate regulation of flow
The keyword that made the difference was "tube" which was critical to locating it since nothing about the clamp was obvious to me to have anything to do with tubing.