What style bobber is this? I’ve looked before and just couldn’t find the name for it.

Found this in a pile of wood a few months ago while out fishing and figured it’d be better in my tackle box than in the ecosystem. I’m especially curious what this kind of float is called, as well as how I would rig it onto my line. From what I can see, there aren’t any holes in it, so it’s not inline, and the only point of attachment that I can see is a spring at the bottom end of it.

Thanks!!