Extruder

Extruder drive gears are the small gears in the extruder. Since these gears are constantly pushing filament into the 3D printer, wear occurs on the teeth. This degrades the filament feed, resulting in a less smooth print. The extruder drive gear is usually easy to replace. By loosening the small hex screw, you can remove the worn gear from the stepper motor and push the new gear on.
If you're repairing a closed extruder unit like a Bondtech, be careful when opening it due to the springs inside.