This Hyperco helper spring has a 2.50 inch inner diameter and a 4 inch free length. It is made from high-quality steel. These Hyperco helper springs are soft springs are used on suspensions which can travel farther than the chassis spring. When the suspension droops, these springs expand and take up the slack between the chassis spring and the spring perch. This keeps the chassis springs centered on the perch and prevents the ride height from suddenly changing. These short coils have very low spring rates and are coil bound when the suspension is loaded. They will not affect the rate of your chassis springs. It is approximately 1/4 inches long when compressed.