This is not true. Try running your windshield wipers without the rubber. Although, it may be true that glass has a hardness greater than most metals, this doesn't mean it won't get scratched. The problem is that it also fractures easily ( sometimes at a microscopic level ). The tiny chips embed in the metal surface and that scratches the glass. This is a multiplying effect. Also, most oxides of metal are harder than glass. And lastly, the quartz windows of the EPROMs are harder than glass. I think he was talking about the glass on the scanner. Dwight