This is a ProMag® .40 S&W STEEL 12-round magazine for Sig® Pro pistols.
These combat-ready magazines are built from heat-treated steel with impact-resistant polymer baseplates and chrome silicon internal springs, for maximum reliability and durability. Sig Sauer® PRO handguns have long been on the cutting edge of polymer pistol innovation. Engineered to meet or exceed Sig factory standards for perfect fit and function, these ProMag magazines come with a lifetime replacement guarantee—ensuring you’ll always have a working mag on hand when you need one.