IMG 9mm Steel-lined 17 Round Polymer Magazine for Glock 17,19,26 review offers the following information;Providing a high-value alternative to expensive factory Glock magazines, Korean made Glock magazines are perfect for rough use, tactical drills, and any other application that might put aggressive wear on magazines and equipment. These 9mm extended Glock magazines are built with the same polymer and steel design as factory Glock magazines. Designed for use with Glock Gen 3 or later. Internal springs are made from heat-treated chrome silicon wire, and like many new extended magazines might need to be loaded and reloaded several times before accepting full capacity.