My Mr basic is almost completely assembled now. As many of us, I ran into difficulty with the axles of the front wheels.
The copper (chromed yellow copper in my case) tubes would not fit over the end of the threading. I filed the blank down a bit, but were not very careful. The threading is not very high quality. The nut will sometimes slip over the threads. Some people glue their wheels onto the axles. I tried to solder the nut in place, using my electronics soldering iron (15W also made in China).
After cooling down, during reassembly, I discovered the tube was too close to the "shaft fixer". This causes problems with the alignment of the gears. So I reheated the solder and adjusted the nut. After cooling down again, it was permanently fixed at the exact right position.
You can see what a horrible soldering job it is. The solder did not flow into the nut. Next attempt (hope not) I will use some soldering flux acid "S39".
To prevent heat damage to the plastic parts, I clamped my axle in a giant heat sink, which I improvised of course.