Source of 1/2" BSP tap (as in thread cutting)?

I'm shortly going to replace all my radiator valves with TRVs and drain-off lockshields and reckon that it's probably a good idea to clean up the threads in the rads to get rid of accummulated gunge (dried up Boss White etc.) before screwing in the new tails.
Any idea where I can get a 1/2" BSP tap (plug rather than taper) for the purpose? It doesn't need to be exotic, and won't be cutting new threads - just cleaning up old ones. The sheds and local PMs don't seem to sell them - nor do Screwfix or the likes of BES as far as I can see.
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Cheers,
Roger
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http://www.toolstation.com/messages.html?codeI495&mainWin=1 should be enough I would think.
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In an earlier contribution to this discussion,

Thanks - but that's just a wire brush. I'm really looking for something which actually screws into the thread and cuts out all the accummulated crap.
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Cheers,
Roger
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Roger Mills wrote:

Try street markets and the like. Lots of old taps/dies etc from specialist purveyors of dead men's sheds' contents...
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http://www.tapdie.com/html/bsp__taps.html
or Ebay
-
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Cut a couple of longitudinal slots down one of the old ones - that should act as a tap to clear out any gunge. Perhaps better still get an iron fitting and do it to that. Although brass should be ok.
BTW, the drain off lockshields work only for the pipe side if you close the lockshield. IIRC.
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*I couldn't repair your brakes, so I made your horn louder *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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In an earlier contribution to this discussion,

Possible, I suppose - and this *is* a DIY NG! <g> But I think I'd rather have the real thing.

No - the other way round. The drain *always communicates with the rad regardless of whether the valve is open or closed. So close the valve to drain the rad while keeping the water in the pipe, and open it to drain the pipe as well.
--
Cheers,
Roger
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On Fri, 16 May 2008 14:26:33 +0100, Roger Mills wrote:

That's what i would expect also.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Try http://www.tracytools.com/ If they can't help nobody can.
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