Phenomenally well made magazine assembly. It is an OEM Glock base magazine with a B&T extension, spring, and I'm assuming their own follower as it is different from my totally OEM Glock 20 mags. Just be aware, these do not lock up in a Glock 20 pistol. So, not an issue, but do not expect interchangeability like with the Kriss mags. Love them though!