Why?

Agreed - it seems odd that no-one seemed to define a standard. Or if they did, it didn't stick.

The big forged "wrap around" compression spanners seem to work on all the variations, but yup there is a fair amount of variation for a a "standard" nut!

I've also come to the conclusion that Aladin self bleed valves are crap. They work when new and not afterwards after draining a radiator, which was removed 3 weeks ago and the valve has had a long time to dry out.

There do seem to be issues with AF sizes generally, when I worked for Racal we used to get large quantities of nuts but we in the end had to specify af sizes as some designs meant that the bigger ones left no room for a spanner and in any case as it was military equipment it had to all be the same. No point in the middle of a battlefield trying to pop down to toolstation to find an alternative spanner!

Brian

Marvellous things when there's space to use them.

Yup... I also keep a couple of those horrid flat pressed steel spanners in the toolbox for the cases where there is no space.

I'm gradually acquiring a set of ground down open jaw conventional spanners.

If the question was "do plumbers carry a set of thin spanners"? The answer is no, they just use more plumbers mait:-(

Compression fittings are never done up 'tight' so even if the available spanner is a bit slack, so what ?.

The pegeler website says tighten nuts less than 15mm by 1 complete turn and 3/4 turn for 15mm and larger. That's after finger tightening.

There are always adjustables that set themselves, for those with deep pockets -

I have car spanners. BSW, Unified and Metric all about this size. Can usually find one that fits. But not always.

Thickness is another problem. With most adjustables being even thicker.