does anybody know what the codes stamped on the front disc stand for I thought it was the year, but if so what does S9 and B0 stand for on early six bolt discs ??
It's the Showa era dating system. 49th and 50th years of Hirohito's reign as Emperor.
The months aren't necessarily correct though as the letters don't denote months but batches as there are more than twelve date code letters on the discs