Help with Seat clamp

Well it looks like someone notched it for a traditional seat post clamp, so you could measure for that try it out. The cut looks like crap, idk if this is worth it.

Idk if the bolt really worked and if it did, it probably needed a special seat post to prevent slippage. Even if you did that, if be worried that the bolt would shear. To find that, measure the hole and try metric pitch threads first. I think you can get a kit of bolts. I have not had the best luck with my thread gauge but that’s probably a user skill error.

That slot was hacked in the frame after the fact. I did a quick Google search and none of the bikes with this frame show an external clamp. I suspect that threaded hole has something to do with an internal post clamp.