One of my struts had that nut on it. It was the only one without an aftermarket strut in it. All the others had the octal headed nut. I used a pipe wrench and a length of pipe. It was really tight.

I have a small pipe wrench but it doesn't seem to get any grip. I might have another crack at it tonight. I'm trying to get a hold of a mate at the moment if I can get a hold of him I'll take it around and show him tonight.

Thanks for the reply all the same.