ProMag Pistol Magazine Glock 21 .45 ACP 13 Round Black 1 Pack DuPont Zytel Polymer 13RD. It is constructed of DuPont Zytel polymer with full length steel internal insert injection molded mag follower and mag spring formed from chrome silicone wire. Specifications for ProMag Glock 21 .45 ACP 13 Round Pistol Magazine: Manufacturer: ProMag Gun Make: Glock Gun Model: Glock 21 Caliber: .45 ACP Magazine Capacity: 13 Round Color: Black Fabric/Material: Polymer Number of Rounds: 13 Package Contents: ProMag Glock 21 .45 ACP 13 Round Pistol Magazine What firearm models does the manufacturer say ProMag Glock 21 .45 ACP 13 Round Pistol Magazine is compatible with? The manufacturer says that ProMag Glock 21 .45 ACP 13 Round Pistol Magazine is compatible with Glock 21ProMag GLKA14-13RD: Pistol Magazine Glock 21 .45 ACP 13 Round Black 1 Pack DuPont Zytel Polymer