QA1's Mustang II Pro Coil Kits feature polished and chrome plated springs. They have a 3.5" upper I.D. and 2.5" lower I.D., these springs have an 8" free length and are offered in four rates. Made with the highest quality materials, QA1 springs are strong, consistent and have a long life. All QA1 springs come with a lifetime guarantee to remain within 2% of their original free height and rate, so you know you're getting quality springs with QA1. Chrome Silicon Steel (CrS), All QA1 springs are manufactured using the highest quality materials for high strength, consistency and long life. Cold Wound - Heat Treated - Shot Peened, All QA1 springs go through intensive manufacturing processes to ensure consistency, accuracy and durability. Squared Ends, All QA1 springs are ground at both ends to ensure straight, consistent and accurate operation. Protective Coated, The Mustang II Springs are polished and chrome plated for the ultimate in appearance. Lengths and Rates Marked, All QA1 springs are clearly marked with the free length of the spring and spring rate for quick and easy identification. LIFETIME GUARANTEE, All QA1 springs are lifetime guaranteed to remain within 2% of the original free height and rate under normal operating conditions.