On cars with catalytic converters, the air/fuel ratio must be measured before the converter by installing the sensor in a bung welded into the exhaust pipe. Vehicles without catalytic converters can use this clamp to mount the sensor in the tailpipe. This clamp is designed to hold the sensor to the correct depth in the tailpipe. Without it, the sensor may give slow or false readings due to suffocation or too much clean air around it.