I calculated just that if you want to use euros you have to use 0,05 €. They are in relation to almost the same size as the Quarter. Only 0.13 mm too thin. so.. u have to scale this whole thing down to 87,59274526%. I do not know which one is the most significant: the thickness or diameter? If the thickness is not essential, then € 0.50 coin is almost the same as the diameter of the quarter.