1939 Notice the double boltholes !!	1939	1940
1942	1945	1946
1947	1947	1948
1950	1951	1951
1952	1952	1953
In 1954, the D code was moved to the suffix position. This was the only year this was done.	1954	1954
1955	1955	1955
In 1956, the standard 6 x 12 size was adopted.
1956	1956	1957
1957	1958	1958
1959	1959	1959