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 extended 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. Holcutters Feature the Patented Quad-Lead Thread System for faster cutter changes. Arbor supplied separately Part # 2634100. Four individual threads on the arbor allows the cutter to quickly be threaded on or off the arbor. Arbor is for use in 3/8" or larger drill chucks. These Holcutters are for producing holes from 11/16" up to 3" dia. in sheet metal, rubber, gasket and fiber materials, and some plastics up to 1/8" (3.2mm thick.