For what it’s worth when I purchased an extruder upgrade I had to get a new motor. The motor on my Ender 3 pro had a press fit gear on the motor arm and it was too short to fit the dual gear extruder (I did manage to get the press fit off only to realize the arm was too short).

If you’re able to order from Amazon, or a similar store with a decent return or exchange policy, I’d just get what you think you will need and return or exchange as necessary.

Just to check I understood you correctly:

You want to replace your extruder and you bought an extruder without stepper motor. Now the original stepper motor has a gear press-fitted onto the shaft instead of a flat side. Correct so far?

There are two things you can do:

• Flex/dremel the gear off and use the tool to cut a flat side into the stepper
• Buy a new extruder motor
• Send the new extruder back and get a good extruder including a new extruder motor

The first option is easy, but requires a tool.

The second option is also easy: You'll just need to look for a Nema17 motor, that's basically it. It should not be a pancake (=flat/small) one, because they are not powerful enough. Low stepping angle (0.9°) is advantageous but not required. You are going to have to tune the extruder steps per mm anyways, since it won't be exactly like your old extruder, so it hardly matters whether the difference between old and new is small or large.

The third option will yield the best returns. These cheapo single-small-drive-gear extruders without gearing are just bad, especially if you add the loss of control you get if you run a bowden system.

If you can spare a little cash, get something like a TBG S or TBG Lite. They are both equivalent, just have slightly different mounting points.

Compared to the stock extruder, these are a massive improvement.

They use a tiny NEMA 14 motor, which weighs much less than a NEMA 17 that is used by the stock extruder. This does allow using it in Direct Drive configuration without adding a lot of weight to your print head.

To have the same (or actually more) power than the stock extruder, they use a ~11:1 gear reduction. They use dual gear drive, meaning that both gears that contact the filament also push it. And lastly, they use really large filament drive gears, which means that it's got a much larger contact area on the filament.

With a TBG Lite I can extrude really soft, flexible TPU with about the same quality and speed that I was able to extrude PLA before. The amount of control is incredible.

And btw, when you swap equipment related to the extruder, you need to do an e-step tuning afterwards. Google what that is.

If you want to pull the gear off the end of the stepper you have there's gear pullers you can print that will do the job, other wise just match the size mean 17 40mm. Just make sure to check the point on the motor when you get it to make sure it matches what creality has going on.

Are you trying to replace your extruder assembly or just the extruder stepper motor? If just the motor, what is making you want to replace it?

If you can afford it just nuy a stepper motor neman 17 make sure the connector is the same. Get a 3 pack they are all the same.