I've entered the dark world of ISO pipe thread designations. For instance I have a plumbing fitting with an R 1/2 thread and one with a G1B thread.

Am I right in saying that 1/2" and 3/4" brass fittings will fit these respectively?

And what does the R, G and B stand for? And what does the 1 in G1B stand for?

G = Parallel thread
R = Tapered thread.

G normally needs a washer or something to seal properly.

That's what I thought but supplier of fitting said 3/4".

Edit: this data sheet also it refers to it as "G1B (R3⁄4)" http://kamstrup.com/media/16684/file.pdf

Edit 2: and there's also "G3/4B" thread designations on page 16 of this document: http://kamstrup.com/media/16718/file.pdf

Posted By: Shevek: “inside of thread is about 30 mm and outside of thread is about 33”

That matches within reasonable measuring tolerance with the page Triassic references above:

http://en.wikipedia.org/wiki/British_Standard_Pipe

Nominal size: 1"
Minor diameter: 30.292 mm
Major diameter: 33.249 mm

PS, pick up a £8 set of digital calipers from Lidl next time they have them. Only used mine half a dozen times but they've been very handy when I have.

http://www.hotukdeals.com/deals/digital-vernier-calipers-7-99-lidl-473355

PPS, cross-posted with Shevek's edit.

PPPS, what's the plumbing fitting? A flow meter?

ugh, not out of the woods yet.

The thread on compression fittings are generally 20 mm deep, whereas the thread on the meter fitting is only 13 mm. So I can't screw it on far enough to make contact with the EPDM washer.

Are there fittings out there with a shorter thread? I can't find any. Will an end feed female iron be any shorter?

Thanks Ed. This meter is turning out to be more hassle than it's worth.

Nahhh - you guys!!! All you need is to wrap some pipe thread string (do not use the tape), I use loctite 55, and then add a thin bead of pipe thread sealant (works anaerobically) - not really needed but so cheap and simple that I always belt and braces with it. As usual with plastic/metal, don't cross thread or apply huge force. Ditch the seal - it's only there because it is easier.

The easy way is to take the item to your local independent plumbing merchant and ask them.... The bit will cost more then at screwfix, but the saved time is worth it.

Ta, useful to know as I'll likely have a few pumps and things with these sort of connectors.

What are those cylinders for, then? They say 1" BSP. Tapered threads?

I believe you can use Yak hair to seal the threads:

http://sethgodin.typepad.com/seths_blog/2005/03/dont_shave_that.html

Posted By: ShevekIs this what you mean by pipe string? http://www.plumbcenter.co.uk/product/jet-hemp-dispenser-80g/

No def not!!! Look here:
http://www.loctite.co.uk/pipe-sealing-9886.htm
The small space left might disturb the water slightly but it will be inconsequential.
Paranoia is creeping in here: Keep it Simple!!!

So you're relying on the fibre washer to seal between the mating face of the plastic meter and the inside mating face of the Union. So basically a std tap or flexible hose type thing. Problem with fibre (and rubber) washers is they are often not a good fit - yes even 'right over' you will cover some or most of the mating faces but fibre washers are also very sensitive to how much pressure you apply when tightening them as they rely to some degree on getting wet and expanding to make a HP seal, rather than filling all the space. I can tell you that when you open up those joints you will find the fibre seal was not central and has shredded when you tightened it. My advice is always to use rubber seals (exception is when supplied as part of a professional grade pump union) and, initially at least, tighten such that the seal is horizontal so as to give the best chance of it staying central.

Too late now but there is no such thing as too many gate valves. Sadly I notice there is no valve on the furthest right CW pipe. So that's a lot of draining before you can get to the thing. So don't be cheap and quick about this: cut that lowest copper pipe where it runs horizontally towards the right wall and fit a valve while you are at it - remember this is a cheap chinese meter....

Win some lose some - but learn every day....nice tidy work btw!

I really hate PTFE tape - once you use the PTFE string you'll kick yourself for not having started with it sooner. That word compound worries me a bit - are you sure it is a anaerobic sealant that is a slightly viscous liquid, often blue, usually called a thread sealant or thread lock.

I guess you just messed up with your PTFE tape. Done right the thread lock isn't needed.

My first plumbing job was installing a 40kW wood burner, 2500ltr TS and all the associated gubbins; never had a problem at 3am mind but I didn't install enough gate valves or 3-part fittings so 1/sometimes getting stuff apart is a nightmare and 2/one day I might have to drain down a couple of thousand litres of water with several hundred pounds worth of anti-rust in it - scary, very scary.

You are going to make a significant effort with the pipe insulation etc I assume - I realise it is inside the envelope but still loads of benefits to putting some effort in.

Okay, I've swapped the meter out for a length of pipe for now. Tempted to leave the bloody thing off. All it's there for is allow us to monitor leaks between here and the footpath (and to monitor water use more conveniently).

I'm using two types of compound: jointing compound, which I've been using on the end of the pipe with compression fittings. And pipe thread compound, which I've been using in conjunction with PTFE tape for threaded connections (including the aforementioned failed joint). I'll get some Loctite 55 and hopefully that'll do the job (shame it's a bit hard to get hold of).

Wasn't planning on insulating those pipes. I'll see how it goes with condensation on the cold ones and maybe change my mind.

Thanks for your help guys.