Sometimes the pulley and stepper motor tolerances work against us. To prevent issues later, we want to check the fit before installing anything. Take the Nema14 rotation stepper motor and the GT2-16 pulley. Check that the pulley drops easily to the shaft. Do not use any force; the pulley might get stuck and then we have a problem. If not, carefully file the inside of the pulley or the motor shaft until the problem is gone.