The Ultimate Safety Plunger replaces the factory safety plunger, for a smoother trigger take-up and extended service life.The part acts in the same manner as the original, blocking the striker channel and prevent the firing pin from moving forward unless the trigger is manually pulled to the rear. The USP improves upon the original by smoothing out trigger take-up, while maintaining timing with aftermarket trigger systems. The USP is machined from 440C stainless steel, with a hardness of 48-54 Rc. Fits small frame Glocks.