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.
The old school ones were actual plumbing parts screwed together, and modern iterations use NPT threading to this day. Probably 1/2"
