A Sure Fix for Loose Screws
To secure a machine screw that keeps coming loose, add a few drops of superglue to the screw’s threads. Put the screw back in quickly; you have only a few seconds before the glue sets. — Joe Patto
Note: If you may want to remove the screw someday, use a removable thread-locking product like Loctite Threadlocker Blue 242 instead.