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Correct, it is a specialised nut, as its pressed and has thread compressions,Nope they can't it's a specialised nut. He has mentioned this already. But you can use a standard nut as the top nut.
So there's two nuts for the strut. One the locking nut is at the top which holds the strut into the car the other is the strut top nut. Both are the same height but the upper one is a locking nut. The only reason the upper nut is thin is so you can fit the little black caps on which is why some shocks just give you a standard nylock nut for the upper.But the Op said " Stuffed a strut top nut getting it off " so one would assume he is means the actual TOP Nut.