This is a Glock 17/19/26/34 PMAG 27-round magazine from Magpul.
Crafted from durable polymer, these extended magazines are designed to meet the same strict standards as your factory Glock magazines for superior quality and reliability.
Magpul PMAG magazines are the gold standard for polymer combat magazines the world over, combining rugged and lightweight construction with rock-solid, all weather performance. These PMAG GL9 magazines offer enhanced capacity for all your double-stack 9mm Glock pistols and compatible carbines.
Like most extended Glock magazines, these PMAG GL9 magazines come with especially stiff springs, which might make them difficult to load the first few times. If you have trouble reloading, consider using a speed loader or leaving them half-loaded for a few days to “break in” the springs.