Flush fit for Smith & Wesson 9mm M&P (does not fit the single stack S&W M&P Shield). Extended 21-round capacity Base plates interchangeable with ETS line of 9mm double stack magazines. ETS mags won't crack or break, are resistant to heat, cold, UV and harsh chemicals - won't become brittle over time. ETS mags come with enhanced features like non-tilt followers, creep-resistant feed lips and clear body allowing you to see count and ammo type - leaving nothing to chance. Advanced Polymer Benefits: Extreme Impact Resistance - won't crack or break when dropped Very resistant to harsh chemicals Superior heat, cold and UV resistance - won't become brittle over time even when exposed to harsh environments or extreme cold Translucent body - allowing you to see your ammo count and type Creep resistant - the feed lips and body won't spread when being stored long term even when fully loaded