A good way to protect the protruding thread of a bolt/nut under the car or anywhere you have access is to use some heat shrink, cut the heat shrink at least 5m-10m longer than the thread, once heated use some small longed nose pliers to pinch the shrink together to seal the end as in the photo below, which is an example.
it should help stop the end of the thread from rusting thus helping in the future to remove the nut or bolt as hopefully no corrosion as taken place.
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