Hougen 14009 Holcutter Arbor for Quad-Lead Threaded Cutters is for 3/8-inch chucks. Use the 14009 Arbor and the 13007C pilot drill for all Holcutter sizes. 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. The Holcutters, are not hole saws. Theyre 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.