ATTENTION: be very careful during the tightening, check the nut orientation and DO NOT use excessive force, you can break this part.
⬢Insert the M3nN nyloc nut in the X-end-idler.
In case you can't press the nut in, don't use excessive force. Leave the nut for now and proceed with the other components for this step.
⬢Insert the 623h bearing into the X-end idler.
⬢Secure it in place using an M3x18 screw.
Now, if needed, use the M3 screw to pull the nut in.
⬢Place your finger on the bearing and ensure it can rotate freely. If needed adjust the screw.