7mm nut or dinosaur poo

Probably would have been easier to get the Dino poo.
Found out nut was missing from tensioner on diesel pump belt when I went to replace pump shaft seal. Never realised how hard it could be to get a 7mm nut. Tried tucks and 3 other nuts and bolts places. Last stop was all metal fasteners in finglas, they also don't sell them, but clever fellow behind counter knew he had a few somewhere. Nut sorted.
Was trying to find out which engine I have, called fiat, Citroen and Peugeot , no one recognised chassis or engine number.
It a 2.5 non turbo, has two belts on drivers side of engine. One timing, other pump.
Looked over whole engine and couldn't find any numbers etc?
Any ideas ??
Have a photo but I dunno how to post it

Never knew a 7mm nut existed. When you say 7 mm is that the diameter of the bolt it is attached to or a 4mm nut that takes a 7mm spanner?

Any engineer that spec's an oddball size nut (M7 or other) as part of a product design is just being an akward pr*ck...

D series Kubota engine exhaust studs use 7mm nuts if I remember correctly..Google for local Kubota dealers if you are stuck..
Steven..

thanks lads, got one in the end