What type of plumbing connection is this?

[Guffy]

Looking to cross this connection over to 15mm compression, but a bit confused by the the fibre ring within the threads, can anyone advise what kind of adaptor I need please?

[guindilias]

No idea about the fibre ring bit - what exactly are you using it for? Do you need the wheelhead valve bit or would an isolation valve do it?

[dhutch]

Is it 3/4 BSP, like and washing machine or outdoor tap connection?

[Mr Pointy]

It's not something like a gas valve is it? I don't know if the threads are the same as plumbing fittings.

[miroku1]

Not easy to tell from the picture but I’d guess it’s 1/2 inch bsp . Is it for a caravan cold water supply ?
1/2 inch female iron to 15mm compression fitting will sort it available anywhere, put ptfe round the male thread , 20 wraps and tighten

[Guffy]

It’s the water supply kit for a Grohe toilet, could just make up my own isolation, but Made sense to used what is supplied. It does look like 1/2” BSP or equivalent to that size, just never seen this type before.

[guindilias]

If so then that's probably so sealant won't need to be used when it is tightened, and so less chance of the sealant making it's way into the toilet.
Could be some obscure Grohe only thread, but more likely to be a BSPP one - you won't find that at Screfix, you'll probably have to go to a plumbers merchant - I've got elbows that size before for a bath tap so you may well find one of those.
If not, then I would just put something inline like a washing machine valve - is the far end a mad fitting, or just an ordinary tap fitting like most toilets?

[Guffy]

The braided hose that came with the isolation valve looks like a proprietary connection to me, the other end of the the hose is the same and connects to the cistern.

[guindilias]

Yep, not sure of scale but that looks like an M10 fitting to feed the cistern, and a (guessing) 1/2" BSSP, maybe a 3/4" BSSP - a 1/2" will need something like this - https://uk.rs-online.com/web/p/compression-fitting...

But I would take a trip to your local plumbers merchant to check the size. Small place, dusty, old man, probably blind in one eye.

Or just order both sizes from RS and use the one you need. And replace the brass olive in the compression end with a copper one.

[Lord Flashheart]

Probability is you'd need a 1/2 female to 15mm compression fitting, which is pretty straight forward. The brown ring will seal it, or should do! If there's plenty of room, I'd simply put a 1/2 flexible tap connector to push fit 15mm like the usual John Guest type. Ideally, take the tap fitting to the plumbers merchants to try before you buy.

[guindilias]

They do make the adaptors for a reason...

[bod27]

Lord Flashheart said:

Probability is you'd need a 1/2 female to 15mm compression fitting, which is pretty straight forward. The brown ring will seal it, or should do! If there's plenty of room, I'd simply put a 1/2 flexible tap connector to push fit 15mm like the usual John Guest type. Ideally, take the tap fitting to the plumbers merchants to try before you buy.

Spot on, its just a std female 1/2” bsp fitting that’s needed, Grohe and most of the other cistern/ frame manufacturers all use a similar fitting.