Spring has superior durability and replaces the stock spring in Ford 9" rear ends with Detroit Lockers. Hypercoils are manufactured from the highest quality chrome silicone steel and high tensile chrome silicone steel available in the world. The material used in producing Hypercoils undergoes two separate magnaflux inspections. Once before manufacture and again after coiling. These inspections insure the wire is free from surface imperfections which, if gone undetected could lead to spring failure. The life of a suspension coil is directly related to the design and materials used. Hypercoils are designed to be as light as possible with maximum deflection and at the same time endure the stresses of the extreme conditions common to motor racing. Because raw materials are ordered in mill-runs and not ordered from a mill's regular inventory we are not constrained to designing from stock wire sizes. Having a larger range of wire sizes available allows our engineers to be design specific for each application. Hypercoils are designed and manufactured to retain their rate and free length for several seasons. a properly designed and manufactured spring will not lose free length under normal racing applications. Hypercoils are manufactured on state of the art equipment using the latest technology by craftsmen who take great pride in producing what we feel are the best springs available anywhere in the world. The manufacturing facility has the capability to produce almost any size or design of spring either cold-wound or hot-wound coils. To properly test a spring to determine rate, the spring must be deflected with both ends remaining parallel. Portable rate checkers commonly available are not reliable. At Hyperco we have invested heavily in computerized scale test equipment to insure accuracy and consistency. Our scale has the capability to rate test a spring through it's entire deflection in . 100" increments and print this data in both tabular and graph form. All Hypercoils are powder-coated a navy blue, the mean rate is etched into the end coil and they are packaged in reusable tubes for convenience and easy identification.Pit Stop USA offers Hypercoils Detroit Locker Replacement Spring - Ford 9" Rear Ends Only LOCKERSPRING at low everyday prices. Be sure to check out all of our products from Hypercoils including Hypercoils Differential Parts and Accessories.