OK, I've seen all kinds of stuff on here, but that's the first time I've seen the spring mod, and I remember teabags and blue foam...
*toddles off to figure this one out*
The spring mod was a way to turn a 510 cartridge into a tank, instead of having the cartridge filled will filler material.
You would put a small piece of filler or blue foam on top of the springs, to hold the liquid back but still touch the bridge so it would wick.
The first spring mod was a spring put in the cartridge vertically, but in the picture I used to very tiny springs horizontally.
They are sitting on the ridges that the 510 cartridges have, which keeps them from getting pushed down.
It was a royal pain in the ....