2 1/2 Centimes - Willem III / Adolphe / Guillaume IV

Luxembourg's smallest bronze denomination across this half-century span passed through three successive rulers because of the peculiar dynastic accident that separated the Luxembourg and Dutch crowns in 1890. When Willem III died without male heirs, the Netherlands passed to his daughter Wilhelmina, but Luxembourg's semi-Salic law required a male successor — bringing the Nassau-Weilburg line's Adolphe out of thirty-eight years of political exile in Germany to claim the grand duchy at age seventy-three.

The unbroken KM#21 type number across all three reigns reflects how little the coin itself changed while its issuing authority shifted twice.