Product review (2 stars): Intentionally limited lifespan
Whirlpool intentionally includes two defects in this part:  1) plastic and 2) square hole.  The fan must be removed in order to replace the motor, but nearly always is stuck to the motor shaft such that the square hole deforms under the pressure to remove the fan.

I put it on slightly loose, and now the fan squeaks.  I fear tightening it more because I don't want to damage the square hole.

Whirlpool could have extended the metal shaft in a way you could torque the metal shaft with a metal tool, but the metal tool on plastic leads to a deformed hole and breaking the fan out until the metal mount is exposed.