I'm looking at propellers today. I've sourced a tiny DC motor, which I'm running without proportional controls because I cannot tell the difference in speed at 3.3V. Also the motor driver I chose allows only for ON/ OFF operation. Seems like proportional controls give extra complication without much benefit. 

Hobby propellers have two markings, the first one is the diameter size that it makes while spinning, the second one is pitch.

The pitch controls the speed of the propeller. A higher numbered pitch means that the blade cuts faster into the air, and moves the aircraft faster. 

The following is taken from RC Airplane world: the two arrow lines represent the path of each propeller tip. You can see that the higher pitch prop (eg 10x8) takes only one and a half turns to cover the same distance that the lower pitch prop (eg 10x4) takes 3 turns to. So, with both engines and props spinning at identical RPM, the higher pitch prop will travel further in the same amount of time - hence a faster flying plane.

Thrust is the force needed to push the blimp through the air. The diameter of the propeller is related to this. The larger the diameter of the propeller, the slower the motor will run, the harder it will work, and more thrust will be created.