I use them to write on polished silicon wafers. They work fine for me. I'm deducting a star because the tip easily detaches from the grip when you try to remove the rubber protection. It seems a bit dangerous as the tips are very sharp. There are others at Revain where the handle can be rotated to tighten the tip. I believe they sell 4 for $13. They're better, but they're half the price.
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