This unit adds capacity to generation 4 & 5 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.Note: will fit glock 17, 19, 26, 34, 43, 45, 48, 22, 23, 24, 27, 35, 31, 32, 33, 37, 38 & 39 gen4-5.Caliber: 9mm LugerCapacity: 2rdFinish: BlackModel: Magazine ExtensionMaterial: PolymerType: Grip ExtensionModel Fit: G17 Gen4-5Brand Fit: GlockCapacity: 2