This holds a standard size drink cans and will mount to most bikes either in the middle of bars with a 31.8mm diameter (most bikes, including road) or to one side of most non-drop bars using the 22.2mm clamp. Some hardware will be needed, I used some metric nuts and bolts I had lying around, see below.

Printing:
The holder itself prints upside-down in one go. Support is needed however, not only underneath the flat section, but also for the pegs that connect the concentric rings. This support is very easy to get out with a knife and tweezers once the rings have been broken free and loosened up. I used hexagonal infill at 35%, I'd say that's a minimum.

As for the clamps, all parts should be printed so that the circles lay flat and the layers are in the optimal direction. Once again, support is needed, but with care is not hard to remove.

Assembly:
Once the necessary parts are made and out of support, assembly is straightforward. One larger bolt (M5 or similar) and accompanying nut to connect the rings to the clamp and either 2 or 4 M3 bolt/nut pairs are used to secure the clamp. Its very easy to mess things up when affixing the smaller nuts, so be careful and use one of the small bolts to pull them into place.