ProMag Roller Follower Polymer AR-15 5.56mm Rifle Magazine 20 Round OD. It is constructed of DuPont Zytel polymer with anti-tilt roller follower and mag spring formed from chrome silicone wire. Specifications for ProMag Roller Follower AR-15 5.56mm 20 Round Rifle Magazine: Manufacturer: ProMag Fabric/Material: Polymer Magazine Capacity: 20 Round Caliber: 5.56x45mm NATO Gun Make: AR Platform Gun Model: AR-15 Package Contents: ProMag Roller Follower AR-15 5.56mm 20 Round Rifle Magazine What firearm models does the manufacturer say ProMag Roller Follower AR-15 5.56mm 20 Round Rifle Magazine is compatible with? The manufacturer suggests that ProMag Roller Follower AR-15 5.56mm 20 Round Rifle Magazine is compatible with AR-15ProMag RM-20-OD: Roller Follower Polymer AR-15 5.56mm Rifle Magazine 20 Round OD