I thought copyrights protect literary and visual illustrations, but not any underlying processes, mechanisms, or artifacts they describe (patents protect those). My understanding of copyright law is surely flawed, and perhaps the “original work” standard means that only descriptions of systems are copyrightable and not the systems themselves.
In that case I agree that my examples fail. Keys and clutches are mechanisms and filling gas is a process, and those aren’t copyrightable (but they are patentable). The file format example fails too, because the concept of laying out data in a particular way is a mere idea, and ideas aren’t copyrightable either (they are also not patentable, though a description of the format is copyrightable and a specific process for reading or writing the file might be patentable if it were nontrivial).