Reading this thread Maslow 4.0 to 4.1 upgrade - Old spool too tigh for new arms got me thinking.
I’m in the midst of re-assembling my 4.1 kit with M3_16 mm screws in the arms, which fit very nicely, to try to reduce friction and thereby improve accuracy (another thread for the results). Even with the long screws and the arm assembly just held together it seems very tight; I can barely turn the spool (of course it only moves a little way before it is stopped by the gears to the motor). During assembly the spool is tight on both the arm parts even when separated.
It seems that I should reach for the sandpaper too!