This is a simple filament spool holder that hangs on a closet rod, or for that matter any rod. The side locks on to the shaft via a 45 degree turn.
This was designed in mind for my MMU2 unit. Allowing me to better feed filament from above.
For wider spools there is a 6in version available here: https://www.printables.com/model/165011-closet-rod-filament-hanger-6in
The author marked this model as their own original creation.