I had to open a 40mm castle nut which was very tightly threaded. I purchased this tool to give it a try since I had run-out of other options.
Looking at it's pins and the slots on my nut there was a difference of ~1/2. It did fit on the nut but I thought the pins would break when I force it....I was proved wrong.
This is the toughest tool I have seen with a very solid construction and because of plastic sleeve on the handle it doesn't hurt hand.
I feel I made the right choice buying this tool.