NOTE: Re-posting someone else (TheRuttmeister)'s thing that he had been taken down (formerly thing:7907), because it should be up. Not doing this out of disrespect for him or his right to take it down, but when I'd downloaded it before it was under the CC-BY-NC-SA license, so I have the right to share it again here, and choose to (rather than just hide away my own copy and hope I don't lose it). Sharing it under the same license.
A spacer that allows you to mount a spool of plastic from Ultimachine on an 8mm rod.
Updated version added, now had bolt holes to allow you to clamp the bearings in place (mine kept falling out).
These instructions are from TheRuttmeister's original item:
Print 2 spacers.
Press fit the 2 608 bearings. Add some M3x15 bolts and nuts to help retain the bearings.
Insert the 2 spacers into the spool.
Stick the spool on the 8mm rod.
You'll need to supply your own 8mm rod holding device! (Something that hangs off the back of your cupcake might be nice).