Yes, first number is diameter, second is pitch.

In general, higher pitch will give greater speed, or larger diameter will give you better vertical pull. However, there are limits to what prop any given engine will turn efficiently.

For example, a decent 46 two stroke may turn an 11 X 7 at decent rpm's giving okay vertical and fairly fast top speed, but you can't stick a 13 X 9 on it and expect it to fly very well. It's just too much prop for the engine.

Therefore, if you increase the pitch for faster top speed, you need to decrease diameter to keep the engine running in it's "efficient" range, and vice versa (larger diameter for better vertical pull means reducing pitch).
Dennis-