The reason we’ve supplied a 10mm axle is because almost all bike axles are within 1mm of the standard 10mm. It’s important that it’s a very snug fit to prevent the axle from spinning and we didn’t want to risk delivering to anyone an axle that is loose and might cause damage. That’s why we’re asking you to file off 0.5mm from the flats of your axle such that it will fit your forks.
Firstly, check the orientation of the wheel such that the flats of the axle are between the forks.
If the motor wheel axle is too large for the bicycle forks, increase the gap by a millimetre or two by removing some material with a file. Do not attempt this for carbon forks.
Alternative instructions for adapting the motor axles:
File the flats of the axle until they fit your forks.
Check fit within the forks, don’t file too far
You may also need to file the torque washers on the sides until they fit within the forks.