If that's a rivet, it's unlike any I've seen before because of the three slots. That's okay - I just get to learn another new thing.
It's also quite large, unless I have the scale of the handle wrong, but that makes sense for the purpose.
: a rivet cannot reasonably be tightened
: ... but you can drill it out and replace it
: ... but the use of any kind of rivet suggests that the inside is not accessible, so replacement with a bolt may not be practical, and a large blind rivet is hard to install.
I did a Google search for like images and found nothing like it. That doesn't mean much - this type of Google search doesn't seem to work very well.