Any one know what locking wire is and what it's used for?

Its a thin wire (Stainless Steel is best) that's often used in aircraft to ensure that things cannot come undone. Typically a couple of small holes in the nut/bolt are wired to the next nut in such a way, that if one loosens, it would pull the other one tighter. Since they are torqued up in the first place, then it's difficult to pull the next one tighter - so one can't become loose. It tends to prevent the first loosening, and definitely prevents escalation.

It's been used on aircraft for years - simple and so so effective.

An example



This is a good solution for wheel nuts, I'm thinking of getting my nuts drilled

On the downside, it can really hurt when you don't bend over the locked wire and you stab it down behind your thumb nail