Glock OEM (factory) current production +2 magazine extension will add 2 rounds to all the standard (hi-capacity) 9mm, 40 S&W, 357 Sig. magazines. Adds 1 round to 45 GAP magazines. Fits all Full Metal Lined (FML) magazines. Works great for G26,27 & 33 magazines. Includes 1 extension and 1 insert. Does not fit Non Full Metal Lined (NFML) early production magazines. Does not fit 45ACP or 10mm magazines. Will not add 2 rounds to any of the reduced capacity (Clinton) 10 round magazines.