Torsion bars
 

I was looking at replacing my torsion bars. And I was wondering if both sides used the same bar. Or if for each side I would need a different bar.

One side is longer than the other, so they are different.

They're getting pretty hard to find new, but remember that they came in trucks with a "1" or an "11" for the spring code on the door jam sticker, and they also came on 5.0 Ford Explorers. Used bars are always a gamble though, as even the #1 bars will sag over time.