> Is this US product [Kroil], in UK terms, WD40, does anyone know?

No, the two products are completely different.  I have been using Kroil
for years, as one of the members of the local clock club was selling it
by the bottle.  I guess he went for the 55 gallon drum.

Kroil is what is used to loosen the rusted bolts on bridges and large
machinery.  It really works well.  My dad left a lawnmower to rust for
a few years.  I was able to get the blades off, which had been buried
in damp soil for that length of time.  I have also used it on garden
furniture and patio equipment.  It takes a day or so to penetrate, and
a bit of force, like with Vise Grip pliers, to release the rusted up
nut and bolt.  Often there is no rust on the threads proper.

Kroil is also gentle enough to use on rusted clock and watch screws.
It takes only a few drops on a watch oiler.  I got the 1/2-pint bottle
to take apart a rusted tower clock, which has lasted years.  I also
used it on the Wurlitzer roll frame that I cleaned up for my Caliola.

Water Displacement formula 40 (WD-40) was designed for releasing
ice-frozen automotive locks in the Northeastern states.  It is an
abrasive: silicon carbide, I have been told.  The idea is to abrade the
ice and from the lock.

When used dry it will turn brass into a fine powder.  Back in the 1970s
my dad used it on a cuckoo clock.  I still have said clock, which has
a fine layer of brass dust on the baseboard.

I used WD-40 once on a dry lock -- the key nearly melted and when I
took the lock apart it was full of brass dust.  It's nasty stuff when
used incorrectly.

I have, however, found a practical use for WD-40.  That is when I am
drilling or milling aluminum and do not have a mist cooling system.
A few squirts of WD-40 on the tool and it stays cool and cuts sharp.

Do keep in mind that WD-40 displaces water so, like Cosmoline jelly,
it is more of a preservative than a magic panacea.  Keep it well away
from anything brass.

Julie Porter