Pinion on a 5mm shaft.. is there a trick?

[Trick440]

Ok I tried putting a pinion gear on my Nue motor 5mm shaft...

I think the pinion set screw threads where messed up already... I was just screwing it in not evenb tightening it and the treads came out.

What should I do when I get a new pinion.... should I grind a flat spot on the 5mm shaft so the set scre can screw in more?

This sucks cause I wanna try this thing!!!!!!!!!