How can I connect a 4mm or 6mm stepper motor D shaft to an old Technic gear?

I would like to mount an old 8-tooth gear to a 4-6 mm diameter stepper motor shaft.

Lego part: 3647:


Stepper motor:

Electric motor

Potential solution found on 3D Printing StackExchange.

Working solution: enter image description here

2 Answers 2


I did find this pattern for a 3-D printer.



For 6 mm shaft the hole used to accept LEGO Technic axle is slightly less in diameter than 6 mm. So you may try modifying one end of of Technic connectors (some examples below) to fit the motor shaft and use usual Technic axle on the other end of connector.

6538c - Technic, Axle Connector 2L (Smooth with x Hole + Orientation)

enter image description here

6538b - Technic, Axle Connector 2L (Ridged with x Hole x Orientation)

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.