5/16 magnetic nut driver is better than commonly spread M8 driver. Usually reffered as "8 mm nut driver" is not exactly 8mm but "about" 8mm. It is not exatly because screws are not according to the metric standard but according to the imperial one. 5/16 is the perfect match for to your screw. It prevents wobbling and makes easy screwing at an unconvinient positions or screwing very long screws.