For the metric machine screw M series the outer diameter does not need a table:
M3 is 3mm outer diameter, M4 is 4mm and so on :)

Also the thread is linear to the outer diameter, M6 having 0.5mm per turn as standard.

You seldom use anytning else than standard threads.  Unusual threads are written like for example M10x0.5  meaning 10mm outer diameter, 0.5mm per turn.

That notion is when you refer to the thread, but when you order a screw named M3x20 that means it is 20mm _long_ including the head if it is countersunk, excluding the head otherwise.

(I think you can write M10x0.5x20 to include both thread and length)?

For US different threads i have no clue though!
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Morgan Olsson, Kivik, Sweden

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