Compression fitting thread confusion!

Getting rather confused about compression fittings and thread sizings.
Take a 15mm straight coupler, e.g.
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts ˆ231&id921
The internal diameter if the fitting is obviously 15mm, to take naturally 15mm pipe. But what is the thread size on either end?
Now take something like:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 341&ts907
This is described as Female Iron Coupler Compression Fittings 15mm×½"
The 15mm must relate to the internal diameter and I guess the thread size is the same on one end as the stright coupler. But what does the 1/2" relate to? The internal diameter on the other end or the thread size?
Help!
Graham

Graham Jones wrote in message
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The 1/2" refers to 1/2"BSP (British Standard Pipe) thread. This is the thread that would have been cut on old style thickwall water or steam pipe that was 1/2" bore. Looking at modern pipe which is thinner wall and indeed the fitting you have, there is nothing you can measure which will be 1/2"
It is all designed to confuse the beginner - so don't worry.
HTH
Bob

On Sun, 16 Jan 2005 20:09:41 +0000, Graham Jones
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1/2"
Thread size. For some reason all the pipes have gone metric but anything threaded is still imperial. 15mm fittings = 1/2" threads.
Go figure.

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Wonder why that is? What if you get a french threaded coupler? Would that really confuse a UK plumber? :-)
M.

Markus Splenius Wrote:
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Yes, but gues what Frenchy stuff is turning up. Mostly the toile inlets with Foreign thread come with an adapter (USA USE SAME FOREIG SYSTEM) to 1/2". I haven't found a way to purchase them seperately.
15mm compression fittings all have 1/2" male threads on so these can b used without the nut and olive for certain jobs.
The same is not true for 22mm, these do not have a 3/4" thread. What missed oportunity?
Very often parallel threads are made with parallel threads, just use lot more ptfe than usual. Of course for gas the only parallel threa allowed is the Long Screw, but for water parallel threads ar commonplace
-- Paul Barker

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They did once. I thought they changed decades ago but at Xmas I had to replace an inline valve that had been bought only about 3 years previously and found that to be 3/4" bsp while the replacement had the finer thread.

On Mon, 17 Jan 2005 06:14:35 +0000, Markus Splenius
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Confused me first time around, had some turn up on some Armitage toilet cisterns, bloody annoying!

On Tue, 18 Jan 2005 23:50:43 +0000, Lurch wrote:
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It's not so much the thread that is frogified but the size. It's 3/8 BSP which is not a common size in UK plumbing.
The 15mm-3/8"F couplers are becoming more widely available.

On Wed, 19 Jan 2005 21:27:01 +0000, Ed Sirett
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I sussed that eventually, unfortunately I'd already positioned the 15mm x 1/2" angled service valves accordingly before plastering the wall up! The proximity of the male thread to the edge of the rear of the pan cased a few difficulties too, I thought that was the problem to start with then realised that the thread wasn't 1/2" BSP.

Graham Jones wrote:
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The reason for all this is that I am trying to determine whether this:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 341&ts907
is the same as this:
http://www.screwfix.com/app/sfd/cat/pro.jsp?idv620&ts 117
but without the flexible hose. Do both items have the same diameters and threads?
Thanks,
Graham

On Sun, 16 Jan 2005 20:26:38 +0000, Graham Jones
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Yes.
DG

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Well very nearly Derek. The flexible connector will be designed to fit on a basin tap with the seal being made with a fibre washer (very likely to be supplied in the pack) onto the annular end surface of the tap thread. The 15mmx 1/2"female iron fitting will screw on a tapered male thread on a pipe or other fitting and will be sealed by the thread jamming augmented by PTFE tape or bosswhite &hemp.
Hope this helps
Bob

In an earlier contribution to this discussion,
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Yes, they both have a 15mm compression fitting one end and a 1/2" BSP female thread at the other end.
However, I'm not sure whether the sealing arrangements of the 1/2" BSP bits are the same as each other.
There are two different ways of sealing threaded joints. One uses parallel threads and a washer - as in a tap fitting. The other uses a long parallel female thread, and a slightly tapered male thread. The second sort actually seals on the threads when the tapered bit is far enough in, using PTFE tape or Boss White and hemp wound round the threads.
I suspect - but am not sure - that your first reference is designed to screw onto a tapered thread. The second one (the flexible tap connector) is definitely parallel, and seals against a face, using a fibre or neoprene washer.

Graham Jones wrote:
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Thanks for everyones replies, a lot clearer now.