Here is a simple filament rack I made that includes holes for a 3/8" metal bar. The Fusion 360 file is included in case the size of these holes needs to be adjusted. If using the 3mf, the part has been divided up into halves so as to fit on your build plate.

Filament: PLA
Supports: None
Brim: None
Walls/Top/Bottom Layers: 3