Removed the stock springs and inside the coils is a rubber type insulator about 4 inches long. One spring had the part installed about two coils from the bottom, the other had it more towards the top and it was also creased/folded some. I removed both to put them in the new springs, but the folded one is a little deformed from being creased/folded rather that circular. The manual shows them but doesn't explain what they are or what their function may be.
I think they may be to dampen noise or vibration, other than that, I have no idea. The don't look like they perform any function related to the actual movement of the spring and seem to be too short to serve as a bumper. They are not installed in any particular position but usually end up at the bottom.I can't think of any front springs I have seen that didn't have them (on Fords that is) so they must have some use. I always put them back in when replacing springs so if you decide to leave it out you may find out what it's for.
Thanks... I'll see if I can get some from the dealer... maybe find out the name of the part too!
Update... Discontinued part no longer available.
Don, you have the answer, they're ment to damp audible vibrations in the spring, more NVH treatment.