It is not just the number of leafs but the thickness and the metallurgy. Best to find the actual rating. Worth a call to the manufacturer. Usually the axle will have a tag with the rating or the model number to look it up. I would get springs that cover the full axle rating and maybe a little more. I would have to know the rating not just accept what they happen to have left over from the last job.
Example if they are 5200 axles I would be going 2750 on the springs (2750x2=5500)
Check the springs in the link I posted above.
6 leafs could be 2500 to 3800 rating
