So this is derived from my original spool holder (http://www.thingiverse.com/thing:74050) and is an add on.
I recently purchased some PLA from MatterHackers (https://www.matterhackers.com/) and the Pro series spools had centers that were only 0.75in diameter. They would not fit on my previous design as my spools were not wide enough and they had end flanges that would not fit through the MatterHackers spool.
So I designed a simple tube to replace them. I then decided that I wanted as many of my colors as were manageble to be mounted on the the printer. So I took the lower design and modded it to add a second tier. There are a few other additions that make this a better print than the lower one. Things like breakaway tabs to prevent some bridging issues in places.
It all seems pretty stable and it cleaned up my workspace a bunch!