Which aircraft/powerplant manufacturers use metric hardware?
All use metric dimensions, only the numbers look sometimes rather odd.

This statement is more serious than it might look, in some places you order parts in metric dimensions and they come as 3.175 mm or 12.7 mm.

All Russian (and, by extension, all former East Bloc country) engines use metric dimensions. You only see fewer of them.

I am less sure about French engines like the CFM-56 which uses a GE-designed hot section, but the fully French-designed engines use metric, too.

In the GA world the modern Diesel engines are all metric.