Get glass, dude.

The kind that fits. Nobody is going to be able to tell what kind of diameter and thread pitch that is by just looking at a picture of it.

If I had to guess, probably metric. Clean it out thoroughly, take it to the hardware store, and start test fitting. If you have a thread pitch gauge you can at least figure out the pitch, and if you have a pair of calipers you could measure the inner diameter and take a pretty good stab at the bolt diameter, as well.

This is all predicated on it being a standard thread pitch of some description because the manufacturer was cheap, and not something bespoke because they were bastards.

Don't smoke out of cheap metal. You're going to end up with some lung shit.

Go to a hardware store and in the fasters aisle they will almost for sure have a spot with different bolts to test thread size. Just clean it first to not get resin on everything.

You're looking for this.

https://www.ebay.com/itm/394658009635

But honestly, just grab a glass bowl for $10-$20. It's a better experience.

End cap for pipes, ain't a plumber tho, idk.

could put an acorn nut on top of a threaded joining part

That looks like aluminum....

Don't smoke out of aluminum.

Is this a mariuwana?

Impossible to say from the picture but I'd start with a brass cap with ½" pipe thread.