This Ruger SR9 extended replacement magazine is constructed form heat-treated blued steel with its components molded from Technapolymer. The anti-fatigue spring, helps keep the magazine loaded and ready for years to come.ProMag magazines are designed utilizing traditional stamping and welding of heat-treated high carbon steel. Every ProMag magazine is backed by a lifetime guarantee against manufacturer's defects. Features: Magazine body constructed of heat treated carbon steel with black oxide finish Injection molded magazine follower Magazine spring formed from heat treated chrome silicone wire Made in USA