I've run int this many times. I believe the square opening is supposed to act like a capture nut to prevent the head of the bolt from turning. On rusty and/or old original ball joint cases the nut is held on so thigh that it spins in the opening. I have been successful with a box end wrench but in some extreme cases I've had to result to using a torch to heat up the nut and jam a screw driver to hold the bolt head in place. If that doesn't work use the torch to cut the nuts off. Works every time!