I've just fitted a new thermostat so that I can use smart TRVs to control the temp in each room.
Fitting the TRVs was easy in most of the rooms, but a few have the valve below that none of the adapters fit. I can't identify the valves and I'd really rather not drain the whole system and replace them.
Can anyone identify them?

Fitting the TRVs was easy in most of the rooms, but a few have the valve below that none of the adapters fit. I can't identify the valves and I'd really rather not drain the whole system and replace them.
Can anyone identify them?

