This Magazine from ProMag has a body constructed of proprietary DuPont Zytel based polymer. It features an injection molded magazine follower and a spring formed from heat-treated chrome silicon wire.Features:Fits Glock 21 and 30;Magazine body constructed of a proprietary DuPont Zytel based polymer;Magazine body has full length steel internal insert stamped and welded like the factory magazine;Injection molded magazine follower;Magazine spring formed from heat treated chrome silicon wire