Most holesaws use an arbor that will only fit a drill with a 1/2-inch chuck. Milwaukee sells an arbor that will fit a 3/8-inch chuck. IIRC, it only works with their smaller hole saws, though. If I were you, I'd try searching with Google or Amazon to find what you need.
In my case, I ended up buying a corded drill with a 1/2-inch chuck so I didn't have to worry about which arbor I was using...