Factory replacement parts are manufactured to the exact same specifications and tolerances and use the same manufacturing materials as the original parts. Some parts may require installation by a qualified gunsmith.
Recently Sig has started using a plastic hammer spring base/retainer with a short hammer. spring. This is being phased in across all models. If your pistol has the plastic base/retainer for the hammer spring, the reduced power 17, 18, 19, and the standard 20 lb. are for your pistol.