A component (mounted in the center of the Spring) which cushions the Spring as it is compressed. Coil Spring Insulator.

Coil Spring DamperCoil Spring Insulator

Fits C-Max, Focus

W/O RS.
Suspension Coil Spring - Repair or Replace
Your coil springs are not especially prone to failure, but if they have been cut, clamped, or heated to have the vehicle lowered, your 2006 Ford F-550 Super Duty might benefit from replacing the strut springs. Excessive rust can make the springs more prone to failure. Contact your local Ford service department to have your suspension system evaluated.