These bits are the bomb. Most of these bits I've been told won't last long unless you buy the expensive ones at $25 each. I beg to differ. I have used them several times and have drilled holes in the bottom of many of my pots; up to 4 holes in each pot. All sizes were used and drilling a hole in porcelain was just as easy for some as it was for others. I also drilled holes in the neighbors' pots. I make sure they stay moist and let them cool a bit between holes. When I put them away after drilling drainage holes in all my pots, they looked just as good as when I took them out of the box before drilling. Love this case and that each size has a separate matching pocket hole that they fit. It closes well and is a good size for storage. I am so proud that I can now drill holes in the bottom of my flower pots and I am very happy with the quality of these bits.