Apex Tactical Specialties FNX 45 Magazine Extension, 45ACP, +2 Rounds, Aluminum, .050 L-Key Allen Wrench Included, Black 119-102 The FNX Magazine Base Pad Extension adds two and a half (2.5) rounds to the existing standard capacity magazine for the FNX 45 model pistols. Why is it 2.5 rounds" not 2 and not 3? Apex's mag extension leaves enough space for 2 additional rounds to be loaded" but also enough space for the stack to further compress the magazine spring to allow a fully loaded magazine to be seated with the slide in battery.