An impeller is provided, including a metal housing, a shaft, and a plastic member. The metal housing has a shaft mounting hole. The inner surface of the shaft mounting hole includes three or more contact points, and the contact points are closer to the shaft than other portions of the inner surface of the shaft mounting hole. The shaft passes through the shaft mounting hole and is affixed by the contact points. The metal housing divides the shaft into an upper section, a middle section, and a lower section. The plastic member passes through the shaft mounting hole and is in contact with the middle section.