4.5 millimetres.
Exactly as in the question: 425.8 mil.
about the thickness of a dime
Veintiún mil
If you want to write it out you do that, but to say it you have to say 'un mil'.
45 mil
you could write "un mil seiscientos".
mil quinientos
$198,000,000.00
Mil setecientos
dos mil quince, pronounced [doz 'mil 'kinse] in Latin America; [doz 'mil 'kin̟θe] in Spain.
No, 45mm is 45000 microns
dos mil dies