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 46.5x16mmSize: external thread M18*1.5 internal thread M18*1.5 length 46.5mmMaterial: Stainless steelPackage list: Oxygen O2 Sensor*2