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Always check a drill diameter with your calipers. Just because the drill bit is sitting in a particular hole in a drill index does not mean that it is that size. I have never gotten good resusts with taps that came in tapping sets. They were always junk and produced crummy looking threads. When working with steel it is a good idea to slow the drill rpms down to avoid heating the part as you can work harden the ID of the hole. A common mistake that is made is to spin the drill bit too fast and take light cuts. Just the opposite is required which is slower rpms and a heavy feed.