In the package of the axle came some extra M2x8 bolts I had ordered for the rear wheels to replace the short bolts that came with the axles. As I mentioned before those short bolts were only 1 - 2 threads into the black part and came out rather easily. If tightened too hard they would strip the threads. As you can see one already fell out.
With the M2x8 in place, a strong and secure bond. I also prefer this look better and am thinking of cutting some M2x8s down to 6mm to use on the front wheels.
View from the back with the short bolts
With the M2x8
