* Wheel and axle: A wheel and axle system involves a larger wheel (or cylinder) rotating around a smaller axle. The force is applied to the wheel (or a crank connected to the axle), which then transmits the rotation to the axle. The key is the transfer of rotational force *between* the wheel and axle.
* Propeller: A propeller uses the rotation of its blades to push against a fluid (air or water) creating thrust. There isn't a distinct "wheel" and "axle" in the same way a simple machine such as a screwdriver or doorknob would. The blades themselves are the primary components generating force, not a wheel transferring force to an axle.
While a propeller *is* a rotating device and might use an axle to connect it to an engine, that axle is not part of the core function of the propeller as a machine element.
