Wilson Combat Shok Buff Prevents expensive frame damage when shooting high-pressure, major power factor loads. Replaceable, poly-fiber washer installs behind the recoil spring on any length guide rod. The shock absorbing action stops the slide from battering the frame. Injection molded for the optimum balance between shock absorption and longevity. Replace every 1,000 rounds SPECS: Poly-fiber, blue. 2 Shok-Buffs® per pak. Not for use in Officer's ACP Models