This replace the magazine base plate and internal floor plate.It will add two rounds to the glock m26, one round to the glock m27 and m33 and no rounds to the glock m39.This units will add 5/8" additional length for better control and comfort.*note- only for magazines equipped with double notches for the ambi magazine release (gen 4&5 magazines).Caliber: 9mm LugerCapacity: 2rdFinish: TexturedModel: Magazine Extension GripMaterial: PolymerType: 0.9"Model Fit: G26 Gen4-5Brand Fit: GlockCapacity: 2