OK, imagine that you have a set of stuck ferrules, Your only tools
available are cold and hot water, specifically to pour over the
ferrules, as a pair, not to put on one side or the other. The
question: which will loosen the ferrules and why?

Some considerations: its pretty obvious that the male end will
contract in cold water (no jokes, please) so that part will definitely
loosen if given a cold water bath.

However, the female end is less clear. Think of a donut (as the female
end of a ferrule resembles a donut in cross-section): first instincts
may say to heat the female end to expand it, but when a donut expands,
the hole actually gets smaller. SO heating the female end may make the
ferrule tighter.

So what if we use cold water on the female end. If an entire donut
shrinks, the center hole gets smaller too. So cooling the female end
may make the ferrule tighter also. Hmm...

So which will cause the hole on the female end to become looser/
larger?

--riverman