Am i being stupid? :-D

I have a 4.0 V8 Disco 2, at the weekend i was going to change the waterpump but got stuck at the first stage then it started raining so wasnt end of the world. Basically i bought a fan spanner off ebay i have measured it and it is 36mm spanner but it does not fit the nut. So my question is am i being stupid or did they use a different size at any stage on the disco 2 v8?

I will be having a landy day on saturday changing the gearbox oil and diff oil etc so hoping to do the waterpump at the same time.

Any advice would be apreciated.
Cheers
Neil