What is it and what does it do? and what's adjustable about it?

 

The tubular control arms replace the factory stamped steel ones. If properly built, the tubular arms should be stiffer and control the axle better. The panhard bar holds the rear axle housing from moving side to side under the body of the car, and more importantly keeps the axle from going its own way. If the ride height of the car is changed the rear axle housing will shift sideways under the car. The adjustable type panhard bar can be adjusted to bring the axle back in center.