For example
That goes between my spool (mounted on top of the printer) and the extruder feed. Got a bearing in it so it's nicely free running so there's much less drag on the filament as the extruder pulls it in.
Combined with a spool holder with a pair of bearings
There's practically zero friction on the spool or the filament as the extruder pulls it in. In fact, you should see it wobble when the extruder retracts a little
Both of these upgrades helped massively with an under extrusion issue I had at the start.

That goes between my spool (mounted on top of the printer) and the extruder feed. Got a bearing in it so it's nicely free running so there's much less drag on the filament as the extruder pulls it in.
Combined with a spool holder with a pair of bearings

There's practically zero friction on the spool or the filament as the extruder pulls it in. In fact, you should see it wobble when the extruder retracts a little

Both of these upgrades helped massively with an under extrusion issue I had at the start.