“””””” It doesn't appear to be of much use when the file contains dozens of objects, as do my metric fastener files.””””””

For the file with “multiple objects”, open that file in its own window along with the working file, then use “copy with origin” and “paste part”…

either by right-clicking on the Copy button, or by the keyboard shortcut Ctrl+Shift+C

either by right-clicking on the Paste button, or by the keyboard shortcut Ctrl+Shift+V