Here is my solder spool holder 3D printed on my Bukito. I used some skateboard bearings (608 - 22mm OD, 8mm ID, 7mm thickness).
8mm = 0.315" and 5/16" = 0.313 so I used a piece of 5/16" wooden dowel
And here it is with the solder roll:
I used #4-40 x 3/8" flat head screws to hold it together, but I imagine that M2.5 should work as well.
I uploaded the FreeCAD source files, and .stl files to: http://www.thingiverse.com/thing:515131