Mercury 225 Manual page 35

Choose a propeller for your boating application that will allow the
engine to operate within the specified full throttle operating
range. When operating the boat at full throttle under normal load
conditions, the engine RPM should be in the upper half of the
recommended full throttle RPM range. Refer to Specifications.
If engine RPM is above that range, select a propeller of
increased pitch in order to reduce engine RPM. If engine RPM is
below the recommended range, select a propeller of reduced
pitch to increase engine RPM.
IMPORTANT: To ensure proper fit, and performance, Mercury
Marine recommends the use of Mercury or Quicksilver branded
propellers and mounting hardware.
Propellers are designated by the diameter, pitch, number of
blades, and material. The diameter and pitch are stamped (cast)
into the side or the end of the propeller hub. The first number
represents the diameter of the propeller and the second number
represents the pitch. For example, 14x19 represents a propeller
with a 14 inch diameter and 19 inches of pitch.
a - Diameter
b - Pitch ‑ Travel during one revolution
The following are some propeller basics that will help you
determine the correct propeller for your boating application.
eng
GENERAL INFORMATION
b
23
22669