Hi all. A wee while ago I asked that if the screw holes in my case for a fan were 70mm apart what size fan would that then fit. A (the only) response I got was " Fan sizes are measured by the size of the fan blades.
So if from tip to tip it is 80mm, then you will have 70mm from screw hole to screw hole. A little geometry will let you figure it out :D".

So I ordered a 80mm fan, which turns out to be far too big. Just to clarify - the fan I bought measures 85mm diameter from blade tip to blade tip, and the holes are 83mm apart (measured from centre of holes). So far bigger than the 70mm.

I really didn't think this would be too difficult - is the fan I bought (new on TradeMe) not in actual fact a 80mm fan, or do I need a 60mm fan, or (knowing my luck) some kind of mutant variety only available from a car boot in Puerto Rico?