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, 44 and 45. This product will only fit Generation 4 and 5 frames. Allows for use of factory interchangeable backstraps. (Will not fit 20, 21, 40 and 41 models) Fits on the new Glock M44