Let's say you've got an old nut stuck completely ... to get deep enough to loosen them. In this case, it's time for a different workshop fluid to step in: penetrating oil. When rust is too thick ...

However, if the nut and bolt are very old and oxidation has taken its toll, WD-40 may not be able to get deep enough to loosen them. Penetrating oil — also known simply as penetrant — is ...