The Promag replacement magazine for the Smith and Wesson Shield .40 caliber is made to the same standards as the rest of the Promag lineup. The magazine body is made from heat treated steel for strength and durability, while the baseplates and follower are made from Promags patented TECHNAPOLYMER. The Promag S&W Shield 9rd extended .40 cal magazine uses Promags anti-fatigue spring that allows you to leave the magazine full loaded for up to 6 years without fear of feeding issues. Like all Promag products, the S&W Shield .40cal 9rd extended magazine is covered by the Promag lifetime warranty. This means that if you should ever have an issue with a Promag product, simply return it to Promag for a replacement magazine.