The M&P Shield 9mm +2, .40 S&W +1 Magazine Extender and Grip Extender is the best upgrade you can do with the Shield and Shield 2.0. The MTX Shield 9mm is compatible with factory magazines and installs in seconds. Unlike other extenders on the market, the patented design permits for a consistent internal wall throughout the extender, which is smaller than the magazine tube. The included spring was engineered specifically for the M&P Shield 9mm to allow for unmatched reliability and last round slide hold open. For use with the .40 S&W the extender uses the factory spring. XTech Tactical's MTX line of extenders are simply unmatched for reliability, ease of install Mfg: Xtech Tactical