"Wire diameter, spring diameter, coil spacing, and wire modulus combine into a spring constant - the amount of force required to stretch or compress the spring some set amount. If the spring is designed such that the coils completely collapse before the plastic deformation of the steel is reached, the spring will not break and will take very little set. The further you are from the plastic deformation limit, the more cycles it will last before breaking from fatigue."

Huh?!