bookstar75,
I'll use the 6x3 prop that you mentioned as an example. The first number (6 in this case) represents the size of the prop. It is the diameter of the prop. The prop in our example is 6 inches in diameter. The second number (3 in this case) is the pitch of the prop. In theory the pitch represents how far the prop will move with each turn of the prop. The prop in our example has a pitch of 3, meaning that it will move forward 3 inches for every rotation of the prop.

Unfortunately there is no set prop to use in every circumstance. It can take some experimentation to find what works best with our plane/engine combination. But there are some rules that will help you find which prop to use. The higher the pitch the faster the plane will more. The lower the pitch the more power the plane will have, power is most noticed when you pull vertical. Unfortunately you lose one to get the other.

Hope this helps

Ken