Turn your classic Mustang's suspension into a modern day sports car. Scott Drake's progressive rate coil springs compress under load and progressively become firmer without giving up any ride quality. These Scott Drake springs are suitable for normal driving conditions as well as a variety of auto cross and race courses. Scott Drake manufactures these springs using quality materials to assure performance and a proper fit. These 400-525# Progressive Rate Coil Springs feature a hot wind from SAE5160H, oil quench, temper, water quench, shot peen, preset, 100% load test, ground flat, and black powder coating. Sold as a pair.