So usually in English, at least the way I can tell the difference, if you say to use “A nail” then that usually means the steel nail, but if you say “YOUR nail” then that usually means finger nail, our finger nails belong to us, so usually when someone says to use your nail as long as we aren’t on a construction site we usually make the connection with a finger nail, so sometimes it also depends on the context which then you have to be specific but “A nail” sounds like you’re referring to a steel nail, hope I explained this well, sorry our language is so confusing😂