The highest quality recoil springs from ISMI offered in 13lbs, 15lbs, 17lbs, and 20lbs. Will work with our M&P guide rods to tune your recoil system to the load and the feel you prefer. We recommend these be used with our M&P guide rods. These are not for .45 or compact models. Factory spring weight is 16lbs for 9mm handguns. 24lbs or 26lbs is recommend over the factory recoil spring for 10mm.