+3, not +4 out of the box with 02 mags. - FAB Defense 4 Round Magazine extension for Glock 43

This product still advertises +4 capacity even though the only mags you'll find for the 43 today are the 02 version. 01s haven't been on any shelves I've seen for a while. In order to get the +4 capacity with the 02 you'll need either an 01 spring or a high-power aftermarket spring. I was able to get a long +15% power spring and cut out the plastic indent on the bottom so the spring sits against the bottom of the extension. You can find other extensions that don't have this issue since they supply their own springs, but this one does not. Despite the capacity issues, it's a very good conceal carry extension and does not snag or hurt when carrying in the front. It does look kind of stupid, but if we're being fair so does the stock 43 mag.