The rotor impeller of a pond pump work very hard and often 24 hours a day 365 day a year, although designed with a long life ceramic shaft they will eventually wear and need replacing.
This is a genuine product from Hozelock and is the complete rotor impeller assembly that includes the ceramic shaft and the two small locating rubbers
Genuine Hozelock spare part for the Aquaforce 4000 pond pump
Complete impeller rotor assembly including ceramic shaft and locating rubbers