Idea was to make a bracket with a chuck so the tabletop could be removed easily if we wanted to use the stool. Since we got a kitten recently, this has become part of the kitten highway, which is now much more stable! 

I printed in orange Kiwifil rPETG. Hole diameters are 5mm. I had to re-drill as 

Please find the onshape project I used here:
https://cad.onshape.com/documents/787cc21deccf87644df78a35/w/4240192ab8a9bdf4c21e52fb/e/786a6ece8db3362f804ee696

Feel free to copy and edit!