Pearce grip's plus extension adds capacity to full metal-lined glock magazines for generation 4 sub-compact, mid-, and full-size glock high capacity magazines.This magazine extension replaces the original floor plate and internal locking plate and adds two rounds to a 9mm, two rounds to a 40sw and 357sig, and one round to a 45gap magazine.This unit will not fit the 10mm or 45acp models.It is made from high impact polymer and withstand drop tests at temperatures from -20 f to 350f.Caliber: Grip ExtensionCapacity: Glock Gen4 9/40Finish: BlackModel: Plus ExtensionMaterial: ABS PolymerType: Grip ExtensionModel Fit: Glock 9, 40 Gen4Brand Fit: Glock