There are plenty of arduino holders on thingiverse but not a lot that combine the power of the arduino uno and the mighty breadboard. A friend of mine requested to make a holder that can hold them both and have a visual pleasing but functional design. This is what I came up with.
It will fit arduino UNO's only as far as I now (they have rounded corners) together with a half-sized breadboard. Don't worry about the double-sided tape that's normally on the bottom breadboard. It has been designed to have enough room for it.
If you print this, please click the "I made one" on this thingiverse page.
I printed this (PLA):
layer height: 0.25mm
Print and clean up all the stringing. Clean up the overhangs of the two middle supports of the holder. Carefully slide in the breadboard and the Arduino uno. Make sure the corners of the Arduino are sitting in the little holes in the outside supports of the holder..