The only time I have seen dimension requirements noted as far as handlebars go os for the stem/bar interface. My guess is that most other accoutrements (brakes, shifters, bar ends, etc.) have enough adjustability to accommodate most bar diameters.
In short, it may not matter :-3)
May you have the wind at your back. And a really low gear for the hills! Chris
There is no standardization for inside diameter, this varies considerably according to the material chosen for the handlebar.
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