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I feel like I'm learning a lot (maybe too much) at once
Well, get ready to learn more then

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When I read the OP above I did think/agree with the old british 1p
Just look at the modern day 1p, or most of the UK coinage. Because of many British territories or crown dependencies, where the entire UK coinage has been fitted with local designs. Jersey, Guernesey, Isle of Man, Gibraltar, Falkland Islands, Saint Helena and Ascension and even some pre-Euro Irish coins all have the same specifications as their UK counterparts. Even though the old British Penny was mighty in its variations of appearances, the UK coin influence remains strong today.
Another "supertype" coin I've realised exists is the through-the-history Russian 10 Kopeyek. Despite massive monetary changes, wars and revolutions the coin still stands strong, although I wonder if not production of the modern issue has seized for now.
A small coin of 17.5 millimetres, smaller than a dime, from what I understand started minting in 1798 and has pretty much kept its dimensions ever since, changing designs many times and lost its silver content in 1931. There was a slight thickness change in 1967 following the commemorative issue, but only for that type.