Are an aircraft's nuts and bolts generally either all Imperial or all Metric, or can they be mixed?

This is a low-tech question, but I was wondering about the distribution of imperial vs metric hardware on aircraft.

When current commercial aircraft land at major airports, a mechanic will know which set of wrenches to grab. Still, I wonder is everything metric, or are some commercial aircraft still imperial? Could an engine or some subsystem use one kind of hardware on a plane that mostly uses the other?

What about at a more remote airport visited by a wider variety and vintage of aircraft? Would a mechanic need to go up and check before deciding which toolbox to use?

uhoh
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