Each Glock OEM 9mm 17rd Magazine is constructed from a hardened steel insert encased in high tech polymer to protect the magazine and prevent deformation, even when dropped from a great height. The high quality spring and follower ensure reliable feeding from the first to the last shot. The Glock OEM 9mm 17rd Magazine is compatible with the Glock 17. It also features witness holes on the back of the magazine – one for each round. No more guessing how many rounds are left.