A pump shaft (10; 12) and a pump member (16; 18) mountable on the shaft for rotation with the shaft have respective contact surfaces that contact when the pump member is mounted on the shaft. At least one of the contact surfaces is formed such that corrosion products of the surface are substantially incompatible with the other contact surface so that joining of the shaft and pump member at the contact surfaces by corrosion is substantially prevented. The pump shaft and pump member may be parts of a dry pump.