This is a Pearce Grip known as the Grip Insert, model PGG4MF.
This unit installs in the bottom rear cavity of the frame utilizing the lanyard hole for retention. Fits model M17" 18" 19" 22" 23" 24" 31" 32" 34" 35" 37" 38 and 45. This product will only fit Generation 4 and 5 frames. Allows for use of factory interchangeable backstraps.
Features:
High Impact Polymer
Keeps Out Dust and Debris
Uses Lanyard Hole For Retention