Oren wrote:
....
A little "trick" I learned was to tighten a bolt or nut - carefully -
when it won't loosen. Back it off a bit and then apply a liquid
solvent. It seems to break the grip; allowing the fluid in.

My experience has generally been if it's so "growed together" as to be a
real problem loosening, there's little chance of tightening it either.
The biggest advent for fasteners was the invention of the impact wrench.

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