shane wrote:

Simon H wrote:
If it's a brass plug, then heating it is perhaps not the best option,
brass has a tendancy to melt.

The best method I can see is to file the nut down so it has two very
defnite sides on it, which you can get a big spanner onto.

Alex

The first thing I would try would be to see if it's possible to
'persuade' a six wall socket onto the rounded nut, maybe after a bit of
judicious filing. Then I'd try what Alex suggested and attempt to file a
pair of flats. If that didn't work I would lose patience with the job and
find a big nut that fits over/around the offending plug and weld it on.
Well, I would if it was a steel plug anyway.

Simon H
Thanks for the advice, there are a couple of reasonably flat sides I have
tried an adjustable spanner on, but I couldn't get enough leverage without
the spanner slipping, so I thought I would try some stillsons to get a
good grip with, if not I'll try filing it as you suggest, and use a
conventional spanner or socket.
Thanks
Shane

I've managed to remove it with the stillsons, I used a technique I've used
in the past to get extra leverage. When the stillsons were in place on the
nut I put a jack under the end of the handle, and jacked it up putting a
lot of force on the nut. Not always possible as it obviously depends where
the wrench/spanner is positioned, but it worked this time.
Thanks
Shane