API Filstar Canister Filter XP XL Impeller KitThe Rena Filstar XP4 Impeller Kit replaces your old, worn out or broken aquarium canister filter impeller. Replacing an old impeller is essential to keep your filter running with optimum power and efficiency. Includes rotor, shaft and bearing Fits Rena Filstar XP4 external filter Replaces old or degraded impeller Old, uncared for impellers can result in decreased water flow, poor circulation, and, in some cases, even an unpleasant grinding noise.