Unusual copper pipe size

[GMM]

I managed to get hold of one of them (not held in stock in every branch) and then realised that the threads are the wrong way around, ie the inner thread is 3/8 so would go onto a threaded pipe but not into the (female) fitting. It did show however that this is indeed the thread, as it would take a piece of the scrap threaded pipe I took out of the job. Fortunately my bodge seems to be holding, so I can wait until I can get to the PM in the week to get a 3/8 plug, then take the cut and bodged stub of pipe out where it branches and cap it off properly.

[GMM]

I sourced a 3/8 plug at the PM's today and taking the pipe stub back to its branch should let me plug it off properly now (especially as I sourced a new longer Stillson and should be able to get it off). The blokey in the PM, who is normally a font of all wisdom, insisted it couldn't possibly be DHW pipework as 'nobody would do it like that'. I'm pretty certain that I correctly identified the warm wet colourless stuff that ran in it when you turned the tap on though ;-) If it wasn't all doing the wrong thing in the wrong place, I'd keep as much of it as I could: The pipes are so thick you could as much pressure as you liked through them and they'd never burst.

[Bob Minchin]

I think he was trying to say that using that pipe for DHW is very very unusual. Smacks of a diyer using something he had lying around. lol

[GMM]

Could be - or even a pro using something he had lying around, as th pipe ends are threaded. The main run of this serves the bath (with other things), which would normally be in 22mm/ 3/4", so clearly not an expert job to modern specs.