For optimum reliability with hardball and hot handloads. Improves overall function by matching the spring to the specific loads being fired. A wide range of recoil springs; to match your loads and shooting conditions. Fits 9mm and .40 S&W pistols. Recoil Pak - (1) 17 lb., (1) 18.5 lb., (1) 20 lb. and (1) 22 lb. conventional recoil springs, plus (3) extra power firing pin springs. Variable Pak - (1) 10 lb., (1) 11 lb., (1) 12 lb., (1) 13 lb., (1) 14 lb., (1) 15 lb. and (1) 16 lb. variable power recoil springs, plus (3) extra power firing pin springs. Factory springs: 9mm is 17 lb; .40 S&W is 20 lb. Mfg: Wolff