No, not talking about the grub screw, though thanks for the suggestion. My terminology may be a bit strange, but thinking just like the motor shaft, but instead will be the shaft that comes out of the planetary gearbox
Something likes this, but 5mm shaft size:
The easiest alternative I have found so far is to use a 5m threaded bolt, though this is not as good for supporting the mounting of drive gears. Alternatively, I could potentially use 5mm threadless tubing if I track down or make some sort of mounting coupler.
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Jubal