CZ Custom Mainspring Calibration Kit One Size. CAUTION: If the pistol is to be used in critical situations such as law enforcement or self-defense. Reduction of the hammer spring strength may compromise reliability of the firearm. CZ Custom's testing has shown the 13lb mainspring in combination with a CZC extended firing pin and CZC 2075 Rami firing pin spring will ignite the primers in the factory ammunition that CZ Custom uses. Given variables in ammunition primers reloading techniques your results may vary. CZ Custom is not responsible for your results. Kit Contains 10LB 11LB 12LB 13LB 14LB 15LB and 16LB Springs. Specifications for CZ Custom Mainspring Calibration Kit: Manufacturer: CZ Custom Gun Make: CZ Size: One Size Gun Type: Pistol Package Contents: CZ Custom Mainspring Calibration kit CZ Custom 30165: Mainspring Calibration Kit One Size