Ball-Bearing Spool Saddles for 3D Filament

While this isn't a particularly new approach to building 3D filament spool holders, this design is simple to make and is 100% printable, except for the 22x8mm or 16x8mm ball bearings. These bearings are very common and readily available on eBay for 35-80 cents each, depending on the particular seller and quantity.

The Single-Width versions require the larger (22mm OD x 8mm bore x 7mm wide) bearings, while the One-Size-Fits-All design uses the smaller (16mm OD x 8mm bore x 5mm wide) bearings.