This design reaches into the waaayyy back machine. I have need to put balls on the ends of rods.

This thing is an improvement over the original design I did a while ago. The difference is the shaft has an internal taper, which increases the friction fit the further you push the rod into the fitting.

There is also an opening at the top of the sphere. The intention here is that you can use the opening to put epoxy into the cavity, to give the shaft a bit more bite beyond the friction fit.

An added benefit of the hole in the top is that you can print these standing up, without any support material, even on printers that insit on using support material wherever they can.

The diameter is 20mm, so it fits into the sockets of the original disc socket thing.

The design is pretty darned simple. You can modify the OpenScad to your heart's content. The default fits a 5/16" rod. You can change that parameter to be any size rod you want.

The single .stl has a single instance of the ball. The '9plate' version has 9 of them on a single plate. That makes it pretty easy to print a whole bunch of them at the same time.

1) Print as many of these as you need to fit on the ends of rods.
2) Slip them onto the ends of the rods
3) Push the now ball ended rods into appropriately sized sockets.
4) Rejoice!