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 percent 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.