Good design; However, using the smallest drill (40mm) it took eight hours, double-sharpening the carbide tips and lots of water to penetrate a 10-inch concrete block of the building's foundation and hit the soft rebar only once. That's how it works, only very slowly when it comes to 30-year-old thick concrete slabs. I used a green stone made specifically for sharpening carbide to keep the leading edge of this cutter sharp. If sharpening wasn't possible, it would take much longer.