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If you're going with files, there is no real need for American.
Altough I guess that in the US these are easier to get than german or english files.
All that matters is that they are old enough to...

Of course, if you're sticking it in fire and start hammering, it won't make a bit of difference whether it was hot rolled or cold rolled or precision ground :)

If you're doing pure stock removal,...

You can use old files. They're cheap and easy enough to come by.
You'll have to anneal them of course if you want to work them.
O1 is available in plenty of places. Your best bet depending on your...