oops. Sump ding.

So that you can use them in tighter spaces.

Come on, gentlemen: calculators out!

28mm, which the OP said is too small, is 1.102" in old money 30mm, (too big) is 1.181"

So 5/8 Whit (11/16 BSF) is also going to be too small (1.100")

1 1/8" A/F (1.125") sounds a _far_ more likely bet. 12 quid for a 24" breaker bar will be one of those "why on earth didn't I buy one years ago?" investments, I promise you.

There's an awful lot of stuff out there that does use the ISO standard sizes:

Thread Spanner

5mm 8mm 6mm 10mm 8mm 13mm 10mm 17mm 12mm 19mm

and so on.

Then there's old Rolls-Royces, where all the bolts have square heads...

You don't say the age is, but the Rover V-8 started out with unified threads. Dunno what it ended up with. The sump on mine needs an 1 1/8th AF socket. And they can be very tight to undo. The correct torque setting when replacing is 35 ft.lb.

And wood screw threads.

To be found on every car that comes back from the cheapo paint shop, holding on items of trim where the original fasteners have been lost ;-)

No, they use 'No More Nails' now ;-)