What are those bars??? 1st Gen F body???

[69MyWay]

I see some adjustable looking bars that seem to attach to the rear leaf spring lower mounts and then go forward to the front spring to car mount.

What are those called - who makes them? Benefits????

I am running the fiberglass springs so I can't put a snubber bar that presses on the spring, but I would like to have more than fiberglass between my axle and the push point on the car.

THANKS!