The S&W Shield is a single stack polymer pistol similar to the full size Smith & Wesson M&P Line. The single stack magazine is available in 9mm and .40 S&W and helps The Shield achieve it's thin profile and relatively light weight: less than one inch wide and 19 ounces. Both a short flush fitting magazine and an extended magazine will be available. The short magazine holds either 7 rounds of 9mm or 6 rounds of .40, while the extended magazine carries 8 rounds of 9mm or 7 rounds of .40. The extended magazine also offers a more full grip.
More information on Smith & Wessons site: Smith & Wesson M&P Shield