These units replace the magazine base plate and retain all other factory components. They do not alter the capacity of the magazine. These units will add 3/4" additional length for better control and comfort. This unit replaces the magazine base plate on the M&P SHIELD & SHIELD 2.0 9mm and 40 Cal. This extension does not alter the capacity of the magazine. It adds approximately 3/4 inches additional gripping surface. Features: Will not work on S&W Shield 45 ACP