Reddit mentions of Pony 1 in. Spring Clamp 1 pc.

I'd like to make a contraption like this (the one on the left):

I live on campus and don't own a car, so while I could probably make it out to a hardware store eventually, the easiest thing for me would be to just order the parts I need online, so I'd like to go that route if possible. I'm wondering if anyone here has made something similar, and if so, if you happen to know some of the specifications for the materials I would need. I guess the parts list would look something like (along with my questions associated with each):

-Pony clamps. These look like the right ones. Is the hole in the handle that you screw the plates into already there or do you have to drill that yourself? Assuming it's already there...

-Threaded rod (is that what they're called? All the ones I'm seeing online appear to be quite long) and hex nuts. Does anyone know what diameter I need for these?

-Those metal plate things. Not sure what they're called, but I'm guessing I can find them if I search for a bit.

-The wrap for the handles. What sort of material/tape is typically used?

-Rubber bands. Already have some. I assume there are no issues with them sliding down?

I'd like to experiment with different training methods in order to improve my pinch grip for rock climbing, as this tends to be the hardest grip position to train using more traditional climbing methods. This seems like a potentially cheap, no-tools-required-to-make device that is also compact and portable (unlike, say, pinch blocks and weights). It also seems very versatile as I can not only train dynamic pinch, but static pinch too at varying widths by placing an object of the desired width in between the handles.

Thanks for any help!