Immortan Joe's codpiece is festooned with castle nuts and car emblems. Real castle nuts are pretty heavy, and also pretty expensive! I figured it might be cheaper and easier to 3d print them; I have, for myself, printed one of each size and made a rubber mold which I then pour spare resin from my other work into in order to get a bunch of copies. Nevertheless, I have tried to price these as low as possible so you can pick up however many you feel you need for what you're working on.
Joe's codpiece is a mix of castle nuts in three sizes. This is meant to be the 'large' size. There are also 'medium' and 'small' sizes available.
Please note that the threads modelled on this are purely aesthetic and were not designed to fit a particular dimension or threading of bolt. These are mechanical parts only in appearance, not in functionality!