siamon

I am replacing a lot of the front suspension and ran into a slight problem. I was removing the front (passenger side) lower control arm, to take the axle and ball joint out. In the process of removing the lower control arm I needed to remove the "rear" bracket with two bolts. I began loosening them and the bolt closer to the inside of the car just spins after something became loose. I used my mirror and saw that the bolt is attached to something on the other side of the bracket/frame. It looks like a nut but its completely round and has grooves running up and down all around it. Was this welded on to the frame? Or is this some kind of special nut. Either way it is extremely difficult to reach with any tool. Any ideas? I will attempt to take a picture but its a little hard to reach.