This is a factory Glock 17 Gen 4 15-round magazine, chambered in 9mm.
This Glock 17 magazine holds up to 15 rounds of 9mm in its steel-lined polymer construction. Its witness holes on the back of this Glock 17 magazine allows you to see how many 9mm rounds are loaded or left. Its anti-tilt follower and steel feed lips promise error-free and consistent feeding into your Glock 17 handgun.