Strong knob for Ender3 extruder advance & retraction.

For me most of the extruder knobs you can find on Thingiverse have the weakness that all the stress is metal on a small piece of plastic and they eventually round out and you need to print another. That's not the end of the world but this is much stronger since it is metal clamping to the small shaft and the plastic has much more surface area to grab to since the gear is already essentially the same as a knurled nut.

For this build you will need an old extruder gear with a clamping screw. (It is fine if it is worn out and chewed up from heavy use; a new one would work but is not necessary.) As long as it has a 5mm bore and 11mm outer diameter.

NOTE: This will only work on NEMA 17 motors with a "D" shaped shaft that is longer than it needs to be. Some new 3D printers with the Mk8 extruder are using heat pressed gears on a round short shaft and you would need to swap the whole motor for this knob to fit. But that motor is basically disposable anyway since the gear will wear out in only a couple years, well before the motor, and the gear is not replaceable.

You will need a 1.5mm Allen Wrench for the clamping screw(s). (one probably came with your printer)

This was designed for my Ender 3 but should work on many more 3D printers that use a Mk8 extruder and NEMA 17 stepper motors. Your mileage may vary.