Ventured out to the workshop but cat find the bastard thread gauges, they’re probably still packed up from the move, I can’t even find any fittings to try and screw on, I know where they will be but they’re well buried. I did however managed to extract a nice shiny brand new sphere from my parts shed, but with nothing to confirm the thread but my old tied worn out eyes it does look to be 1/4” BSP.