Cheap filament holder friction reducer.

thingiverse

I experienced skipping on my ender 3's. The extruder skipps because some filament spools don't freely rotate on the holder. There are designs out there that use multiple parts and bearings but I wanted something cheap, easy and functional. It is simply a pipe with a lower poly count inside. I found that it worked better in my experience than if it were smooth. The layer lines made it encounter a lot less resistance.