modified upper body to insert brass threads.

brass insert used: M3*5.7*4.6 amazon link

i used a M3 washer to have a reference so that the insert sticks out by 0.5mm (see in cover image)

otherwise the gears will scratch on the surface and you have an ugly bump on the other side.

Also used loctite to secure the screw with perfect tightness.

I played around with the design of the outer surface to suit my personal taste :)

Here a small tutorial on how to put brass threads: