How to extract only used references from a bibtex file

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I am preparing to send tex files, graphics files, etc. to a publisher. I think there should be a way to send something less than my entire bibtex file to them. Is there a way to easily extract only the references that I am using for this paper into a separate bibtex file or is there some other way to do this? I notice that when I compile the tex file (using Texnicle on MacOS) something called a .bbl file is generated that contains only my used references but is is different from a .bib file. I suppose this is best posted to a latex list. :-/

Jerry