Leaf Spring Code?

[dangerranger33]

Where do you find out the leaf spring codes for explorer and which would have the stiffest leaf springs?

 

[Alec]

I think as the codes go towards "z" they get stiffer. I think the stiffest are W or something. I think those are on the upper-end models with the towing package, but Ford has a habit of not following logic when deciding on what springs to put in