Summary

This is an approximate mockup of the uranium cubes used by the Nazi's to create the first attemp at a nuclear reactor. Unfortunately there aren't a lot of photos for reference so this is probably only close at best. I wish I could inspect one to get more accurate.

More info here: https://www.npr.org/2019/08/31/755478866/have-you-seen-any-nazi-uranium-these-researchers-want-to-know

P.S. If this looks familiar and you have something around left from WW2 that matches this please look at the article above.