Not sure exactly, but I have never taken off the smaller one since I got it!! Much better balance, lighter, and I don't feel like I give up much in depth at all, Yesterday dug a 77 signal, at 8-10 inches..................1937 Wheat pennie. Many, many more will agree with me, I'm sure. The smaller DD should be the stock coil, on the ATP. I have three coils( Both DD's, and the Sniper coil) and the only one I use is the smaller DD