Very common item in the aftermarket for decades, marketed as a way of fixing sagging springs without replacing them. You'd be amazed, when we would caution people against using them as it would raise the vehicle 1-2" but make a harsh ride, they'd go ahead and buy them anyway. What can I say, every set I sold helped the ol' paycheck.
Well, the easiest way to describe the ride is to compare it to riding a rigid motorcycle with an unsprung seat and a 12" over springer front end in an urban warehouse district with old, rutted asphalt and railroad tracks not flush with the pavement. Been there, done that, never again.
that's old school.
they had ones you'd twist into the coils on f-body and 80's g body cars to take up the sag a big block swap would cause in the stock springs if you couldn't find diesel springs to swap in.
'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.