20 Fillér Set Issue

The 1966 composition change from aluminum to copper-nickel for the 20 fillér was a quiet but deliberate decision by the Hungarian National Bank, driven by chronic problems with aluminum coins being mistaken by weight and feel for other denominations in automated vending equipment — a growing issue as Hungary expanded its network of state-run machines through the mid-1960s. The copper-nickel alloy brought the coin's physical properties into closer alignment with what the machinery could reliably read.

Production ran across just two calendar years before the type was effectively stabilized. The KM#550a designation distinguishes this alloy variant specifically from the preceding aluminum 550.