This is a battery cover for an old Cen-Tech Micrometer from Harbor Freight. Odds of anyone else having the same micrometer, a 3d printer, and a missing battery cover are probably low, but what the hell.. Maybe someone can use it to make a similar part.
A lower resolution nozzle would actually probably do a little better. I had to trim it a little bit to make it fit perfect. After cleaning it up a bit with an razor blade, it fits better than the original.
This is, by far, my most detailed and complicated part to date. Took me about 4 iterations to get it right.