FITS TO M 18 mm X 1.5 mm PITCH O2 SENSOR ONLY. This weld-in oxygen sensor nut fits standard 1- up to 5-wire type oxygen sensors and is a must for custom fabricators. It allows oxygen sensor, also referred to as exhaust gas temperature sensor to be attached to the exhaust manifold or downpipe. It is a weld-on, precision machined 18 mm x 1.50 pitch mild steel oxygen sensor threaded ring. THIS OXYGEN SENSOR FITTING WILL NOT FIT TO OTHER OXYGEN SENSORS THREADED WITH SMALLER OR LARGER THREADS. Won't fit to special 14 mm threads! Please check the oxygen sensor thread prior to purchase. Helps install the oxygen sensor on any steel pipe either on factory, aftermarket or tuning exhaust. Welding required! Oxygen sensor nut facilitates easy installation of the O2 sensors and is designed to be welded into any exhaust pipe. It comes with the proper Metric 18 mm x 1.5 mm pitch thread for any OEM requirement or aftermarket oxygen sensor and is backed by 10-year Magnum warranty. It might be required for custom exhaust systems, and is also useful for air/fuel ratio measurements when dyno testing. Magnum Header O2 Fitting is highly durable and matches OE form, fit and function. This unit is put through numerous tests under extreme conditions to ensure durability and high quality. These weld-in Oxygen Sensor Bungs are a must when you're retrofitting fuel injection to your vehicle. They can be placed in the exhaust pipe or header or in any application, requires an O2 sensor. *** Tips for custom projects: Mount the oxygen sensor nut as close to engine a possible, without exceeding the maximum operating temperature for the O2 sensor. Oxygen Sensors located after upstream exhaust system leaks or too close to exhaust outlets are susceptible to poor mixture readings or influence of ambient air. O2 Sensors exposed to exhaust gasses with too high amount of un-burnt fuel can lead to vague - a possible lean - reading.