Puky Wutsch Tow Hitch - Print in Place - Universal

I designed a tow hitch for my kids Puky bike. The ball shape is for a particular other wooden toy in our household that has a 11-12mm diameter rod. I also added some “universal” designs so you can print them or design a custom attachment.

The concept on all hitches it that the outer shape can move / rotate freely around the inner core. It is held together only by a 0.2mm diameter spot that should not even print in real life. Therefore print them without supports in between the two shells or it won't move.

Keep in mind that this model is not designed to be super sturdy and has some planned weak spots. If a kid falls on the hitch I want it to break and not to impale the kid. 

I printed all parts in PLA with 20% infill and 0.3 resolution.