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.
Update – thanks to Solar Mike's answer I was able to locate the exact clamp, apparently still made which is a "Fisherbrand Castaloy Hosecock Clamp" from Fisher Scientific, with the description
Fine-machined adjustment screw for very accurate regulation of flow
Neat!
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.
Best Answer
That style of clamp can be or has been used to compress or close soft tubes or pipes in many situations like drip feed water supply to plants as a simple example.