If you already have the 140mm high Filament Duck spool holder, this cylinder/axle allows you to use more spool sizes and it also lets the spool roll more freely. It should work with most spools not wider than 82mm. Tested with MakerGeeks, Filament Outlet, Sainsmart, Hatchbox, and 3D Solutech.

This one is not quite as easy to use as my other remix: http://www.thingiverse.com/thing:682283 because you have to work to get the axle in place but not too much more trouble than fitting a spool into place on the original Filament Duck. The real plus with this is if you already have the holder, you can add the cylinder to allow more brands of filament spools to work with it… as well as letting the spools roll more freely.

Note that this cylinder is 82mm in length so may not fit the very original Filament Duck… I do not know its dimensions. But you can easily change the height (length) of the cylinder in the scad openscad file to make your own size.