Andy, unfortunately I don't have this tool with me to take more detailed photos.
The hinged arm only goes to 90 degrees, so could well be designed to fit into a hole in the bench, with the thickening forward of the spring a base while it's in that position. It's a solid forging, totally unbranded. When the jaws are closed they could hold a small glass tubing either crosswise or lengthwise the hollows being formed in both directions. The spring pushes the jaws apart.
The hook on the end of the upper arm looks deliberate perhaps if it was mounted on the bench you could tie a piece of string to it and hold it closed with your foot to free both hands for the task.
One suggestion we received, a fishermans fly tying tool. A lot guessed dentistry and some ladies over the age of 50 suggested something to do with testicles.
Cheers,
Geoff.