Thread lock? I’ve heard that mentioned by a friend. Oh, interesting, it is an oil placed in metal screw threads to help prevent them from slipping and unscrewing. So that’s why there’s always a weird oil on metal screws. Or maybe that’s just plain old oil. Well, the photo of thread locking fluid definitely doesn’t look like plain old oil, so yeah, probably not the case.
20191214/https://en.wikipedia.org/wiki/Thread-locking_fluid