This Oxygen Sensor Simulator Fitting comes with adjustable jets. The male end of this fitting threads into your existing M18 x 1.5 O2 Bung while your O2 Sensor threads into the female side of the fitting. You can use the supplied jets to help fool the O2 Sensor and eliminate Check Engine Lights (CELs). The "J" style works the same as the original style but is ideal for ease of installation where clearance is an issue.