Vibrant's Bosch LSU 4.9 Heat Sink O2 Bung is designed to prevent premature oxygen sensor failure. The finned surface has been optimized to improve convective cooling, delivering up to 30% cooler O2 Sensor temperatures vs. a standard bung and the coped design makes welding easier.  This bung only fits a Bosch LSU 4.9 Oxygen Sensor.