Hypercoil Drag Racing Springs are cold wound from pre heat-treated SAE 9254 chrome silicon wire, and optimum wire diameter is used for the individual design. After coiling, the closed ends are ground, and springs are thermally stress-relieved, preset, and shot-peened. Completed springs are magnafluxed, powdercoated blue, and inspected for size and integrity. Additionally, Hyperco tests each coil for true rate and etches it into the spring. Such strict manufacturing standards yield springs with +/- 2% tolerance range (most are within 1%). Sold individually, all springs have 2.5" ID.