20 mm Filament Spool holder for Wanhao Duplicator i3

The axis for the spool holder on Wanhao Duplicator i3 is 30 mm, but some filament come on 20 mm spools. Here's a smaller axis for those. Be sure to print with high wall thickness and high infill density, as the spool is heavy. But you probably also want to print with high resolution to get the threads as good as possible. Also do NOT overtight the nut, as it's very easy to break the bolt. Light finger tight is enough. I have again used Dan Kirshner's excellent threads.scad library http://dkproje