It's a really basic version of a tiny trailer hitch. I wanted to be able to sell it so I designed one quick. (NOTE: This is for display/jokes only! do not actually try to pull anything with this!)

This one should sit flush with your receiver(2" receiver), and uses your normal hitch pin to hold it in place.

The nut might need some tolerance play in your slicer, like .2mm or so, to fit over the ball shaft. I'd use super glue as well to make sure the ball doesn't come off.

Eventually I'd like to make some improvements to this.

 * THE PRINT PROFILE IS ONLY FOR THE 2" RECEIVER VERSION - I HAVE NOT PRINTED THE 1.25" RECEIVER VERSION YET AND DON'T EVEN KNOW IF IT FITS/WORKS PROPERLY  *

I added STL files for a 1.25" receiver version - both a all-in-one version and a separate objects version. 

I don't have a 1.25" receiver so i can't test it out and don't know how to measure where the hitch pin hole would be without one, so if someone prints one out and tests it and can measure that for me so I can make sure it sits flush, that would be great!!