This is a popular question for us. Many manufactures develop propellers of several diameters. The propeller diameter is usually decreased as the propeller pitch is increased. This is true in most all outboard and sterndrive propeller applications. Propeller diameter is the total circle that it makes in one revolution. As the propeller’s aft rake is increased its diameter is reduced. The propellers rake and geometry has an effect on diameter, as such we place more value on propeller pitch than that of diameter.