The cones hold the spool onto a 5/16 (or 8mm) threaded rod and adjust to different sized spool holes. The cones can be easily removed to allow the spool to be taken off. Springs pushing a plunger into the larger end of the cones retain them.

Print two cones and two washers. If you want you can use two nuts to retain one of the cones but I made mine so both have springs.

The rod is 5/16 with two 608 bearings with a nut holding it on both sides on each end. The rod and bearing just drop into place in the wood bracket. The opening on the bracket is away from the printer and at an angle to keep the rod from falling out. The cones can be put on and taken off without taking anything off the rod by just pushing back on the spring. The cones have a slot that allows them to be taken on and off. Just pull the rod out the back side of the holder, pull the cones apart and slid one cone off. Slide the spool onto the rod then put the cone back on. The spring and plunger push into the cone and hold it on.

Part http://www.thingiverse.com/thing:118049 was used to hold the rod onto my Prusa I3 (custom top frame).

Videos:
http://youtu.be/olPRlIk4npY
http://www.youtube.com/watch?v=JlwgfdYHBzU