issue with struts *please help*

[threeplus10]

We are replacing the struts on my buddies hatch & ran into a problem: we removed both fronts from the chassis, diconnected the brake lines, etc. But when we went to remove the damper locking nut none of our sockets seemed to do the trick. The 21mm & 22mm seemed to catch but it would not loosen. What's the best way to remove that nut?? I feel like it is something very simple that we are overlooking!! [really]

[dr.occa]

Use an impact gun. Also, the top of the shock has straight edges on either side just under the threading. It's suppose to key into the top strut mount which helps keep it from spinning when you go to undo the top nut.