Hi Tonia, the M1590 set is supplied with a 9mm ( 3/8″) mandrel that will fit in a standard keyed or keyless chuck of your electric drill. To fit the hole saw to the mandrel, you undo the large hexagonal nut and place the relevant hold saw over the double D flats on the mandrel and then tighten up the nut securely, before inserting it into your drill’s chuck. Dave