The extended base pad for the standard capacity Glock magazine. 3-piece design is easy to reassemble onto the magazine, and can be easily disassembled for cleaning without losing any parts. Does Not Work with 10 round capacity magazines. For 1st-3rd Gen :Glock 17C,17L,22,22C,24,24C,31,31C,34,35 For 4th Gen:Glock 17,22,31,34,35 Technical specs: Adds +5 capacity on 9mm Adds +4 capacity on .40 cal Fits standard capacity Glock 9mm & .40 magazines Additional power spring provided