Actually they burn the carbon out of them by not quenching soon enough or often enough. If you rest your finger on the bit close to the grinding and quench as soon as you feel it getting hot you can do an excellent job on a dry grinder.I think Brownells are the best screwdriver bits you can buy. I have used their thin blades for many years and they hold up. You can grind your own but most anneal the tip by getting them too hot then quenching them in water, this can take any temper in the steel out and give you a soft blade. Regards, Bob
I flinch a little when I think of how many years I've been buying stuff from Brownell's. You can't go wrong there. If for some reason it ain't right, they'll make it right.