Remixed this model so it is shorter, but will still accept standard 1kg filament spools. Also my print of the original (male spool) was fairly loose in the ender bracket. So I added a slight decline angle to the grooves and added a bump for friction. This made it more secure.
Please refer to the original design on Thingiverse for assembly instructions, and needed bearing sizes. I've included the unmodified nut .stl for convenience.
Note: the outer sleeve may be a touch too big in X/Y axis to keep bearing snug. I applied 2 layers of tape around the main shaft towards the end to keep the bearing in place. Do this AFTER installing the first bearing, near the ender bracket.
The author remixed this model.