This is a Wilson Combat Shok Buff known as the Replacement, model 2BGL.
The injection molded polymer WILSON SHOK-BUFF buffer prevents the slide from battering the frame during operation and softens the recoil impulse for faster follow up shots. (Fits Glock models 17/ 17L/ 18/ 19/ 20/ 21/ 22/ 23/ 24/ 24C/ 31/ 32)
Features:
Injection Molded
Easily Replaceable
Prevents the Slide from Battering the Frame During Recoil
NOT COMPATIBLE WITH GEN 4/5