Description
These precision-made hobbed gears are designed to be attached directly to a stepper motor with a 5mm shaft. They grip tightly using an M4 grub screw.
Many direct drive extruder setups are designed to work with gears such as these - see Thingiverse for different designs.
These gears are designed to work with 1.75mm filament, and do so perfectly. They will physically work with 3mm filament, but you will need a very beefy stepper motor.