This. That's why new props come with a set of new screws (and 2 extras) with loctite pre-applied on them. Even the instructions say to dispose of the old screws.
If your re-use the screw for some reason, and you are short on lockite, ask your girlfriend some nail polish. I use it as locktite replacement for old motobike fixing!
Use a toothpick to apply to the threads. Using directly from the tube will guarantee that you put too much on the tiny screw. Touch the toothpick to the tip of the Locktite nozzle and use sparingly.