copper

What sort of fitting is shown in my photo below and is it maintenance free in the sense that it can be buried behind plaster? It certainly does not look like your typical soldered joint or compression fitting. Mine also freely rotates. Fitting before radiator valve: Type of fitting? by eveares...

Complex setup- short version, I've put the pipework in for 2 radiators 'cos I wanted to hide the pipework in ceiling and stud walls, there's no boiler fitted and no rads fitted to the ends of the pipework yet (got to finish insulating the ceiling & let BCO have a skeg at it before I board and...