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I couldn't find anything that corresponds "K" to anything. I went ahead and contacted huskyspring and they told me my leafspring has a 1100 pound rating. Hopefully the guy wasn't guessing. My plan is to swap out the springs and install 1250's.The second one is what I think you want;
http://www.therangerstation.com/tech_library/leafspringrate.htm
http://www.huskyspring.com/Page.taf?title=Identifying Ford Leaf Springs&page=fordsprings
Richard