I made this model because I was building a tree. In the core, four poles were held in place by wooden shelves. I needed something that would attach to the poles and support the shelves, so here it is.

The collars are parametric, so you can adjust the size to fit any size of dowel, although the screws might not be functional below around 10mm of ring thickness. 

It is easier to clear the supports from the half-rings if they're printed with the hinges upward. They also fit better on a build plate that way. The screws come out more cleanly if printed on their sides.