This spare part includes both the bell, which encases the motor, and the propeller. The Motor Bell with Propeller is included with all (Foil Assist) Mast sets and is compatible with all three mast options. The bell easily plugs onto the motor using a strong magnetic connection. Plastic propeller blades are already mounted onto the bell and can be replaced with the stiffer aluminum blades. Note: It is normal to see marks on the inside of the bell after the first use due to residue from the motor. Warnings: Rinse the bell with fresh water after every use. Allow it to dry completely, then apply a thin layer of marine grease or WD-40 Specialist Penetrant (or an equivalent) to maintain optimal performance.