Take good care of the cooling system - change to a new impeller every year!The impeller is a very important security device. Its task is to pump the water through the cooling system of the engine. But remember that the impeller should be replaced every year. And always make sure you get a Johnson Pump Brand original impeller. Then you'll know that it matches your pump exactly.40mm (1.57)Width 19mm (0.57)Impeller article number 09-808B-1MC97 (for cooling)Replaces Jabsco 22405-0001 Europe & USAInner diameter 12 mm