On Sat, 12 Sep 2015 02:05:30 +0000 (UTC), John Doe
wrote:

Part number 6.

http://servicenet.dewalt.com/Product...7&itemnumber=6

It looks like the flats engage matching flats inside the anvil.
Someone who knows hammer drills should be able to tell you if you even
need the flats for your application, or if you can just turn the end
down so it turns freely inside the anvil.

I don't have a hammer drill, so I'm not your guy. But the anvil, I
would think, might be irrelevant for your application.

--
Ed Huntress