This 4 3/4″ combustion blower fan blade is the single-sided impeller that is used on the Harman Accentra Insert, P35i and P35i-C Insert, and the PF120 Pellet Furnace.
If any of the petals (fins) are bent, your stove may vibrate. To fix this, you can sometimes bend them back to help balance the motor. It is suggested to replace the impeller if the metal is corroded, if there is metal missing or if the impeller is unbalanced through wear and tear.
If you are replacing your combustion blower motor for any reason, it is suggested to also replace the impeller. Harman has engineered 3 different sizes for their various stoves which is why they are not already attached to the motors.