An HVAC friend of mine recommended the Milwaukee Large Tapping Nozzle Series for a DIY upgrade of a 112 year old heated floor. - room school. I love learning how the pros work and as any professional electrician and plumber should already know these bits work great but with at least one caveat. For the piping of our underfloor heating, many holes have to be drilled in the old 2 1/2 inch joists and blocked in between. I started yesterday and I'm afraid I got a little carried away. With a powerful angle drill, the drill seemed to stop at nothing and the job went quickly. The self-retracting tip pulled my cutter 1 1/2 inches with ease, and to complete the hole (once the tip had punched and lost grip) all it took was a little pressure on my part. The holes were clean and the chips were everywhere! Nothing will stop this beat I thought. Little did I know that in the 1950's old fashioned cut nails were used for nailing plywood floors. Soon I found one of these nails with my blade and, thinking that this thing would penetrate anything, I patiently waited for it to gnaw through the nail and spit it out along with the fragments. Soon I was struggling with the drill, pushing harder and harder, counterattacking from the other side, giving up, trying again, and finally acknowledging that the "strings" at the tip of the screw had broken. The nail sat right in the center of the hole, straightened and barely scratched. Milwaukee sells its bits with extra tips to keep work going in such cases. But the way I am, I soon screwed up the second tip and the job was only 40% done. And without this tip there is no drilling. I did my best. Do not go. When I came back to the store, they told me straight out: These bits are not for nails, especially the hard metal of old nails. Drive in a nail? Immediately step back and start a new hole where hopefully there is no nail. I love learning how the pros work and as any professional electrician and plumber should already know these bits work great but they are not designed for nails.