Disclosed is a shaft system particularly adapted for use in molten metal applications, such as injecting impellers, submersible molten metal pumps, and others. Embodiments of the shaft system contemplated by this invention very generally including a base shaft with an outer surface, a shaft sleeve composed of material adapted to be used in a molten metal environment, the shaft sleeve having an inner surface approximately corresponding in size to the outer surface of the shaft and located approximately concentrically around the shaft; and a shaft coupler between the outer surface of the shaft and the inner surface of the shaft sleeve; wherein the shaft sleeve is securely attached to the shaft by the expansion of the shaft coupler relative to the shaft and the shaft sleeve.