I need to replace a bit of central hearing oil pipe which measures 10mm
OD.

If I get some pipe and fittings which are quoted as being 10mm, will I
get what I want, or might I get something that is (say) 10mm ID, 12mm
OD? What's the standard terminology? Most adverts seem very reluctant
about making such things clear.

I note that plastic and rubber pipes seem to be referred to by their ID,
and usually both ID and OD are quoted.
--
Ian

On Monday, November 12, 2012 8:24:41 PM UTC, Ian Jackson wrote:

mETRIC SIZES are tubes, the outside diameter is the controlled dimension.
Imperial sizes are pipes, the internal diameter identifies the pipe size.

I assume it's copper. Asking for 10mm should get the right fittings. Browse the BES catalogue on line, they stock nearly everything.

On 12/11/2012 20:48, Onetap wrote:
On Monday, November 12, 2012 8:24:41 PM UTC, Ian Jackson wrote:

mETRIC SIZES are tubes, the outside diameter is the controlled dimension.
Imperial sizes are pipes, the internal diameter identifies the pipe size.


That's a slight over-simplification!

Imperial copper pipes are indeed designated by the *nominal* bore - so
that, for example a "half inch" pipe is very similar in size to a metric
15mm tube. However, all 1/2" copper pipes have the same standardised OD
- so that fittings will fit(!) - and the *actual* bore can be different,
depending on the wall thickness.
--
Cheers,
Roger
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On Monday, November 12, 2012 10:22:46 PM UTC, Roger Mills wrote:
On 12/11/2012 20:48, Onetap wrote:

On Monday, November 12, 2012 8:24:41 PM UTC, Ian Jackson wrote:



mETRIC SIZES are tubes, the outside diameter is the controlled dimension.

Imperial sizes are pipes, the internal diameter identifies the pipe size.





That's a slight over-simplification!



Imperial copper pipes are indeed designated by the *nominal* bore - so

that, for example a "half inch" pipe is very similar in size to a metric

15mm tube. However, all 1/2" copper pipes have the same standardised OD

- so that fittings will fit(!) - and the *actual* bore can be different,

depending on the wall thickness.

Yes, that is why I said the "internal diameter identifies the pipe size", because 1/2" pipe may not be exactly 1/2" bore, but it is still called 1/2" pipe.