Which adapter do I need?

edited February 5 in General Questions & Topics

After easily installing the smart thermostats on all radiators in the house, I got to our bedroom one which had a different (older looking) one on it. I've tried all the included adapters but can't see any of those working on it. I've also spent time trying to figure out what it's called, but it doesn't seem to match any pics I find of all other types.

Can someone advise?

It turns up/down using the 4 sided section it seems, screw hole at the top to secure the plastic head.

Pics attached show the unit, including when the top metal section is unscrewed.