Simple Filament Spool Holder for 608 Bearings
608 bearings are really cheap by bearing standards. For instance, you can get a pack of 30 608ZZ bearings on ebay for only $15 shipped (from China, of course). That's only $0.50 per bearing!
The spool holders I've seen so far either don't have a foot I like, don't use the type of rod I want, or don't use the size of bearing I have on hand. This thing fixes these things for me and if it does so for you, too, great!
I've included the OpenSCAD source and the compiled STL file.