Bar useful to eliminate the risk of reserve or bend the rear leaf springs of any type, essential if you use single sheet leaf spring or SPOA.
The geometry of this system designed and widely used in the US is used to cancel the rotation axle of the bridge protecting the springs and being installed in a central location, not in any way limit the rotation of the bridge twist, resulting in a lightweight alternative, but of equal economic reliability the common traction bar.
IMPORTANT. The bar has galvanized finishing, the photo is being updated.