This bit has the effective length needed to drill through holes in 2 0.5 inch (12 mm) sheets (2 pieces of 0.6 inch (15 mm)). ● When penetrated, the stopper stops the drill advanced, and takes no extra spin time, so the battery lasts longer and allows you to drill more holes with a single charge. ● The groove shape of the groove over half the circumference makes it easy to unplug even when you unplug it, saving your battery.