These O2 sensor extension harnesses are sold in a pair of TWO.
They are used to relocate the front 02 Sensors (AFR) from the stock location to a new location like into the collector when long tube headers are installed. The URD Spec-U Equal Length Long Tube header as well as the JBA and Thorley brands carried by URD have two mounting locations for the front O2 sensors, upper in the center tube, or in the collector. It is better for the front O2 sensor to sample the exhaust from all three cylinders instead of just one.
The stock harness will only allow you to install the front sensor in the upper center port. With these extension harnesses you can move the front sensor down to the collector.
These extension harnesses fit:
2005-2009 4Runner V6
2010+ 4Runner V6 Dual VVTi
2005-2015 Tacoma V6
2007-2015 FJ Cruiser