Adrian wrote:

Not everything uses those few "preferred" hex-head sizes. I use 11mm - M7
- a lot on old Citroens, and they crop up in other places, too. 14mm gets
a lot of use. 8mm is preferred M5, but 9mm does crop up occasionally.

11mm fits small 'f' plugs.

Mind you, since buying an old Land-Rover, I've been pleasantly surprised
at how many Dibnah sockets and spanners I've accumulated over the years.
Gawd knows where from, but I'm not complaining.

I have a lot of spanners from my dad's workshop. Some of them are so big
I wonder if he used to work for Brunel.

Bill