Had to make the trek to the nearest real hardware store to find a M14 x 1.5 bolt. That did the trick. It's all about torque. Ruined my Vise Grips, but oh well.
From the pic it appears those nuts have flats, and they extend quite a ways from the socket. I would have just put them in a vise, and hit the socket with the impact gun in the tighten direction.