Explain: 1. Made of high-quality materials, durable and practical. 2. Don't expand only when the extension doesn't work. This is the built-in real Mini catalyst. 3. When the catalyst is removed, the rear oxygen sensor will display higher temperature and higher flow of unburned fuel. 4. As a result, this throws a check engine light (unit, SES, DTC) with error codes typically p0420 (catalyst system efficiency below threshold library 1) and / or p0430 p0420 catalyst system efficiency below threshold library 2). Off road only . Specifications: Size: about 46.5x16mm Size: external thread M18*1.5 internal thread M18*1.5 length 46.5mm Material: Stainless steel Package list: Oxygen O2 Sensor*1 Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.