For Ford Mustang 1979 to 2004. Every spring produced by H&R comes from the H&R ISO 9001 certified engineering and manufacturing facility in Germany. All H&R springs are produced from a special 54SiCr6 spring steel, which has strength rated at 290,000 psi resulting in unrivaled tensile strength and resiliency.H&R Sport Springs offer the handling characteristics and aggressive appearance that you've been looking for, without the harsh ride characteristics of less-advanced spring systems. H&R Sport Springs feature more control and are engineered for the street, making them comfortable and fun to drive. H&R Sport Springs are crafted from a special 54SiCr6 spring steel to ensure quality and performance