AA to C Battery Adapter Remix
I took jwags55's design, lengthened it to that of a AA (so I didn't have to print two for each battery) and increased the twist (just for aesthetics).
For the hollow model, I changed the wall to .525mm so that I could print it nicely as a vase with my .35mm nozzle.
Also, I uploaded a solid model as requested in the original comments.
Autodesk Inventor source file included for the solid model.
Edit 6/5/2015
I added a double and triple adapter to the lot. I needed this for a flashlight that had three "C"s stacked end-to-end and thought it would be nice to have one continuous adapter for it.