This is Thinkyhead's design of a printable spool holder for i3 single plate and Rework variant 3D printers.  It is copied as is from his Thingiverse repo.  This is what you use for the machines in our bot farm.

Includes Openscad source files so you can easily modify the parts to suit your needs. There are a couple of variations.  We use the i3sh 608 plate on our builds.  You attach M8 threaded rod through the spool holders and fit a 608 bearing to each side of the spool holder.  There are variables defined in the Openscad file to change the spool holders to match the size of your filament reels.  We print the parts in PLA, .3 layers and 40% infill.  We've been using the original design for almost two years.  Thinkyhead updated the designs in summer of 2014.