Adjustable spring rate coil thats also progressive. Sprindex is specifically designed to have a progressive spring rate for the last 20% of stroke for big hit support and for bikes with a linear linkage design.160mm spring length for DH useAdjustable spring rateAdapters included for different size shocks and set upsMade of super high tensile spring steelItem SpecificationsI.D. (mm)38.3MaterialSteelSpring Weight450 - 490Stroke (ins)3