4xUniversal M18X1.5 O2 Oxygen Sensor Test Pipe Extension Spacer Extender AdapterSpecification: These are needed when using a HHO System or a test pipe. They are also used to lean out your vechicle for better gas milage. Dimension: Thread: M18x 1. 5mm Length: 32mm 1. 253 Inch? Material: Stainless steel Fitment: The extender has a 7 8 hex head which is the same size as most O2 sensors and it makes them easer to install not like the straight sided extenders. Fits all standard size sensors with a 1 2 Inch diameter tip. The size of