This is a factory Glock 20 10-round magazine, chambered in 10mm.

This Glock G20 magazine is made with an advanced, hardened polymer with steel insert to protect it from high drops. Also, because of its 10-round capacity, it is compliant with all State laws. 

Its signature Gen 4 black follower provides reliable feeding into your Glock 20 handgun. Like most Glock magazines, it has witness holes along the back so you can see how many rounds you have loaded or left in your mag. Overall, a great magazine for your Glock 20.

Pick up a few spare Glock 20 magazines today!