Not very complex but does the job well. I needed it for some more projects (namely heterogeneous spools, or my spider spool http://www.thingiverse.com/thing:234040 for raw coils)
The STL is for a 8 mm threaded rod, and it embeds an optional nut in the background.
Still, you can customize it for other diameters, you could tailor it for a chopstick, as it would be a good candidate in place of adding a PVC tube as I did. No need to publish tons of derivatives ;)
The customizer on my thumb wheels is useful to set different diameters for the end side (a 75mm one is included)
The openscad source code may prove useful to those who want a robust and parametric hook (constants can be changed also for the feeder hook).
The default diameter is tight so that the rod is held in place without the need for a nut nor counter-nut. I added a specific support to remove because I had some trouble with my fan setup and the (regular) overhang was ugly on one side, you can disable it in the customizer if you really do not want to print it.
A rim helps it stick on the bed. Used 0.8mm walls and 20% infill.
Update: added the main star and counter-nut for large rolls.