Holds Octave Systems spools perfectly, works fine for MakerBot spools also, especially if you make one of these as well:http://www.thingiverse.com/thing:29101Created with TinkerCAD, you can edit it for your own purposes here: https://tinkercad.com/things/7GAviE15YXW?display=gyEp5cLI69EPrint it and bolt it on. I printed it on my Up! in "fast" mode with loose fill and it's plenty smooth and plenty strong. I've printed it with the round side down and with the round side up; not much difference. I do suggest printing it in a horizontal orientation.