The Holcutters, are not hole saws. They're precision ground, heat treated tools that easily cut thru the stock rather than ripping, tearing, and pushing thru as do typical hole saws. They can produce holes three times faster and cleaner than hole saws in sheet metal and have dramatically extend tool life, too. All sizes have a "shoulder" to prevent plunge-thru, which is especially useful when drilling into live electrical boxes. See for yourself why electricians, fabricators, and mechanics prefer the quality and speed of a Holcutter over hole saws.