I saw this step drill when I was wondering what size drill bit to buy. The product description says it can drill any hole I need, from 1/4 to 1-3/8. I was dying to try it when I received the package. The content of the laser marking is very clear and some commonly used sizes are highlighted. The first time I used it with my rechargeable pistol drill, I punched through the protective casing of the junction box. I didn't make a pilot hole because the instructions say it's not necessary. To my surprise, it quickly pierced the iron shell. Then I got a sense of pause from the next few steps as I continued to drill. He told me that the size of the hole is increasing step by step. I quickly finished the first hole and then made a few other holes and finished carving. The bit appears to be intact, except that the coating on the outside is slightly worn. I believe it will take a long time. This is a quality product worth buying.