I got 4 of them and put them on 4, 13 round magazines I selected at random out of the ones I have. 3 went on easily with just the right fit. The fourth was a little loose so I tried it on 2 other magazines and it fit the same. It isn't a big deal because the set screw snugs it up nice. What I did was slip the sleeve over the mag, and run it down to the bottom. Then insert the mag into the gun, (obviously check to make sure everything is empty), to make sure it goes in properly without any resistance, then press the magazine release and lower it slightly and snug up the set screw. Then put it in and remove it several times to make absolutely sure there is no interference. All 4 work as intended, and they really make the grip better, (larger), for anyone like myself who has big hands. I'm going to get a few for my Glock 26. They make them for adapting the Glock 17 mags, and the Glock 19 mags to the Glock 26. I'm going to try both. I'll try and get some pictures up a little later. Bill T.