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?" you ask? The Apex Tactical 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. Expected Results: 1) Adds 2.5 rounds of additional capacity to your magazine. 2) Maintains function of the slide lock after the last round is fired. 3) Finger grooves on the perimeter and front corner finger grooves make gripping Mfg: Apex Tactical Specialties Inc