ProMag Steel Pistol Magazine Bersa Thunder 9 9mm 17-Round Black 17RD. The springs are precision wound using heat-treated chrome silicon wire. Bases and followers are injection molded from polymers selected for their durability. The result is quality consistency durability and reliability. Specifications for ProMag Steel Bersa Thunder 9 9mm 17-Round Pistol Magazine: Manufacturer: ProMag Gun Model: Bersa Thunder 9 Caliber: 9mm Luger Magazine Capacity: 17 Round Features of ProMag Steel Bersa Thunder 9 9mm 17-Round Pistol Magazine Magazine body constructed of heat treated steel with black oxide finish Injection molded magazine follower Magazine spring formed from heat treated chrome silicone wire Package Contents: ProMag Steel Bersa Thunder 9 9mm 17-Round Pistol Magazine What firearm models does the manufacturer say ProMag Steel Bersa Thunder 9 9mm 17-Round Pistol Magazine is compatible with? The manufacturer says that ProMag Steel Bersa Thunder 9 9mm 17-Round Pistol Magazine is compatible with Bersa Thunder 9ProMag BRA-A2-17RD: Steel Pistol Magazine Bersa Thunder 9 9mm 17-Round Black