If you are drilling a lot of arcs in concrete, use this jig. Although one of the bit heads broke pretty soon, I went to Home Depot and bought another compatible bit. A long-stemmed rosette is magical. Another complaint might be that the sockets they give you are too recessed. This is normal when drilling in wood, but hard materials that don't sink will not work properly as the nut will slip off the screw head before fully engaging.