This is a Wilson Combat Shok Buff known as the Replacement, model 2B.
The SHOK-BUFF prevents the slide from battering the frame during recoil by sandwiching a 1/10" thick poly fiber buffer between the slide and frame contact areas. When you are shooting high performance loads in your 1911 style pistol" you want the extra protection that the original SHOK-BUFF provides.
Features:
Good for 1,000 Rounds
Injection Molded
Easily Replaceable
Prevents the Slide from Battering the Frame During Recoil
