I needed to drill a hole in my porcelain enameled cast iron sink for a soap dispenser so I bought these based on the reviews. I wasn't disappointed. As others have pointed out they need to be damp be held when you use them. I built a small dam out of putty around the area I was working and filled it with water. I would suggest tracing the hole with a marker so you have an idea of where it would be should.The only caveat I would like to make is to make sure you have good leverage when using them as the bits will want to slip when you first start.Go very slowly at first until you've dug the first hole to to guide the drill. As soon as you do that, put pressure on it and you will be fine. Once you go through the porcelain, the water will flow due to the gu Iron filings very dark so you can't see what you are doing. I regularly cleaned the hole with paper towels and filled it with clean water to make sure I was still on target. Eventually you will break through and your water will run out. Just widen the dam and let your faucet deliver water continuously and you'll be fine. I highly recommend this product as I am new to these things and have had no problems using them. For those wondering if you need an electric drill, I don't think it is necessary. I just used my cordless Dewalt and it had a lot of liquid in it. And don't forget to put a bucket under the sink to catch the water if you break through or you'll end up with mush on your hands.