lharvey:

listen to CRFlyer he has the correct fix for your question. the pitch is the second number in the prop size.
and this is how it works, the pitch for example in a 12 x 8 prop is designed to pull the plane at 8 inches for one revolution of the prop and a 12x6 would pull it 6 inches for one revolution thus lowering the pitch will slow the plane. by reducing the throttle will obviously slow the plane but the lower pitch will give what seems to be like a breaking effect after using a higher pitch. then going back to the higher pitch will give to feeling you have just put it in netural giving a coasting effect. you may or may not want to increase the length of the prop depending on the RPM's the motor will turn with a given prop. using a lower pitch prop will also let the motor stay more up in the power so when you slow if you should need to reapply power in an emergency it will be closer to the power range needed.
Hope this is clear.

Miloh.