Work great, I've drilled rocks and glass with them..will buy more...

slow and easy gets the job done with any breakage or damage. I use one of those things they make for mechanics to hold nuts and bolts, they are heavy and have rubber coated magnets on the bottom so they don't move around. I use my dermal type tool on low and keep whatever I'm drilling under water in the bolt tray with water in it...:)

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