This is a "screw" that can thread a clockwise and counterclockwise nut. It's just satisfying to play with.

Original idea from: https://youtu.be/cDfMI5ahbJI

Edit:

Some people have asked for various variations of the screw but I haven’t had time to make most of them. I uploaded a longer screw and shorter nuts which were the easiest requests to fulfill. These are untested so print at your own risk, although they should work since I just extended or shortened the original models

There are lots of remixes that might be what you’re looking for so check them out!

Edit 2: I added a cap to seal off the open end of the bolt in case you want to trap the nuts in there. It’s really a tight fit on my well calibrated printer so keep this in mind as you print it, you may have to adjust it slightly to fit properly without it falling off.