If you check almost every spring manufacturers
They make 1 spring...
Example
Reg cab springs drop 2 inches
Ext cab Springs drop 2.25 to 2.5 inches
The aftermarket springs are interchangeable
I have 2 sets of springs currently -
Aftermarket manufact dont want to make 2 different sets of springs
Increases costs and overhead
If you note below
Same spring - slightly different drop
http://www.hotchkis.net/cgi-bin/EDCs...atalogno=1910F

If you check gm - the part numbers for RC and EC springs are different
because of the different spring rate

You can interchange springs
The springs in 03 EC are the same as a RC

 

That's what i thought. Sweet.

 

So if I purchased 2" DJM drop coils for an ext. cab, they would drop my regular cab about 1.25" to 1.5"?

 

In theory, if they have 2 different spring offerings for EC and RC