To push paste out of syringe, we need threaded shaft. There are 2 ways:

• Use coupler and threaded rod
• Use gearbox with built-in long threaded shaft

Coupler with threaded rod

You can take this coupler 2.3mm to 3mm. Use 2.5 mm drill bit to enlarge hole, then tap M3 thread and insert 60mm M3 rod or screw with loctite.

Disadvantage is loosing 20mm of movement length (or increase length of device). Let's leave this for Plan B.

Gearbox with built-in long shaft

There are no ready mini stepper solutions with M3 shafts, but we can assemble it from two donors:

• Mini stepper. Any of this size (10mm) with metal gearbox will be ok.
• Gearbox with 50mm M3 shaft from Brushed NV20 motor (you need 30RPM version).

In may sound strange, but those parts are compatible!

See photo. Donors are on left side, result on right side. Total cost with delivery will be about 10$. Not ideal price, but acceptable, requires zero efforts and is the most compact.

If you decide to combine other components - check gearbox sizes, those should be equal (the most popular can have 10x12mm or 12x14mm plates).

If components go out of stock - we still have Plan B with coupler. Both solutions do not require complicated tools and can be reproduced by anyone.