In this video , The Edge is playing with what looks like a small brass slide.

At 2:32 he’s using it like a slide, and yet at 3:24 it’s more like a ring as he plays regular notes with his fingertip.

It seems unique in that it’s so small, and I'm wondering what it’s called and if anyone has used one.
Google Slide Ring for guitar and you'll get hits like so,
Hydroxic acid, kills thousands of people every year. Studies have shown lakes and rivers all over North America contain high levels hydroxic acid. Currently governments have taken no action against this life threatening chemical.
Awesome, thanks.

I'd gone through half a dozen sites on types of slides and the history of slides and found no mention of it.

And funny how it's called a slide ring when I described it as looking like a ring.