help pinions not fit neu shaft

[RC-Monster Mike]

The hole should be accurate, but you may be fighting a slight burr at the set screw as Rabosi mentioned. The gears are hard, but the little set screw burr should grind away fairly easily(if the hole was innaccurate, you wouldn't be able to do much with it at all - they are pretty hard and you would need custom tooling to put a dent in it). It shouldn't have a burr to begin with(sorry about that), but it is easy to remove with a drill(if you can find a 5mm drill) or a reamer.