deemed unsuitable, 1-3/8" pilot broken in second hole (drilling a flimsy metal bolt with pilot hole pre-drilled) and my 7/8 " is on its last legs after very limited use, a few teeth are missing, the spring doesn't work causing me to have to pick out the metal, which is a big loss of productivity. I was thrilled to have a handy set for my exposure but unfortunately it didn't work out. I'm sticking with my carbide bits on my drill, which I've never had a problem with.