Jon and list I recently put 26mm bars in a 25.4 hole French stem. I used a 1"-25.4 mm flapper sanding wheel, that was 1 1/2" long, and it took about 3 minutes. You need to stop every minute to let things cool down. It makes a straight hole and leaves no gouges to start a crack. Check often with calipers as you flap.
Dickey Greer
West Monroe,LA USA