I need to replace some broken eyeball return jets in my pool, but I'm confused about one of them as it's not a regular threaded eyeball, but it's longer and seems to be either threaded or pushed into the pool wall. I can turn it, but it turns the whole thing, not only the eyeball nut itself since it's not threaded there.

Any help on what kind it is and how to go about replacing it would be appreciated.
Thanks