Well there you go!
In theory, the 7mm is a “non preferred” size under ISO, so might be seen less.
But in reality, as soon as you move away from standard fasteners, and start dealing with flange nuts, studs, hydraulic fittings, banjo fittings - or whatever, all bets are off!
And this is always the problem I have found with metric. I can fix pretty much anything found on a car with about 4 or 5 Whitworth sizes. I need at least 7 to cover the same range in SAE, and about 11 for metric!
In theory you only need about 5 “standard” sizes, but there are too many standards, and too many “specials”.