Fits M&P Shield 9mm and 9mm 2.0. For use with .40 S&W 1.0 and 2.0 use factory spring. Not compatible with Shield 9mm EZMP Shield mag extension adds 2 rounds to both the factory 7 and 8rd magazines. Uses factory sleeve when used with the 8rd magazine. Custom engineered spring. Optimal ergonomics and texture for recoil control. Adds 1rd and requires use of factory spring for Shield .40 S&W