Corrosive currents will flow directly to the zinc in the collar, instead of to the propeller. Protects other metal parts nearby. Your boat's rudder, shaft and other metal components will get the same protection. Guaranteed to stay tight against the shaft.
Some collars ride loose after even a little corrosion.
Patented Godfrey designs won't. Goes on without removing the propeller. New brass design prevents pollution. Brass inserts prevent any zinc from falling off and meet environmental restrictions. Godfrey Corrosion Collars.