Replacement flat wire spring for the M&P 9mm and M&P 2.0 9mm. The standard M&P is equipped with the 15# recoil spring. The 11# spring is ideal for use with suppressors or subsonic ammunition. Use the 13# spring for light target loads.The longest lasting handgun recoil spring made, up to ten times greater service life than a conventional coil spring. Recommended spring replacement at 30,000-40,000 rounds.