Pearce Grip Pearce Grip, Frame Insert, Fits Glock Gen4 20/21/41, Black PG-FI21G4 This unit installs in the bottom rear cavity of the frame utilizing the lanyard hole for retention. Fits model M20" 21" 40 and 41. This product will only fit Generation 4 frames. Made of a high impact polymer" this insert is designed to keep out dust and debris as well as finish off the overall look of the frame. For use with or without the factory interchangeable backstraps.