The System Sensor P48-21-00 Sampling Tube End Cap is a durable HVAC accessory designed to seal the end of a metal sampling tube used in duct smoke detection systems. It works by securely closing the sampling tube, helping maintain proper airflow patterns and preventing dust, debris, and contaminants from interfering with air sampling performance. https://www.partshnc.com/p48-21-00-system-sensor-end-cap-for-sampling-tube