Fuel filter thread
 

Can anyone explain why my terracan has a fuel filter with a different thread to the one listed by all the parts suppliers even though the part number stamped on the filter on the car is the same as the number on the new filter?!

Some filters can be a little tricky to get started and yet be the correct thread.
Were you able to compare the replacement to the one removed?
If all seem OK,just get another filter.

Thread on new filter is M8, thread on old filter is M6. Although the part number on the old MANN filter is WK829/3, the same as on the new filter, the thread is completely different. I've also tried other makes - they all have a much larger thread than the filter on my car.

M8 and M6 are not thread size
It is more about the shaft size or hole size
I have seen two different oil filters recommended for the same vehicle
Looking at the hole size, they were different.
Only thing I can think of is that there are possibly more than one engine available to the vehicle

But, for the same filter to have the same part number???
Don't know.
Also, I think you are talking about oil filter and not fuel filter.

Exactly. Completely different shaft size. And it's definitely the fuel filter - I've already changed the oil filter.

Now a days, most fuel filters are in the gas tank.
They use to be in line from the gas tank to the carburetor or throttle body injector.
But, no sense in arguing. Have you been able to find the filter you need??