I just meant the smaller the radius the more difficult to hollow. The smallest I have heard of anybody using is 4" and 5" to do a double hollow. That would be grind the bottom half of the blade to 5" dia. and then on top of it with a 4 " wheel. Not too many do that. I use 6 and 8" wish I had a 10" . If you look at blade profiles you will see the radius I am talking about. Some of the wedges look like over 18" dia. You can do it with a smaller wheel it's just a PITA IMHO :<0)