A second 50-yen type debuted in 1959, also coined in pure nickel, but at a weight of 5.0 grams, lighter by nearly 10%. The lighter weight would have meant a savings in material costs, but I wonder if the primary reason for this new type—which, unlike the previous coin, was center-holed—was to prevent confusion between the 50-yen and the new silver 100-yen coin that had been introduced in ‘57. Below, the center-holed 50-yen of 1959-1966.
This example is dated Showa 40 (1965), very near the end of the type’s production run. These large-diameter coins were withdrawn and together with earlier nickel 50-yen pieces were melted, and then alloyed with copper for recoining as yet another, smaller, center-holed 50-yen coin beginning in ‘67. (Some of the reclaimed metal was also used for the new copper-nickel 100-yen that was introduced that same year.)....