Date Symbols

1958 - 1972 Record crank arms were not dated on their back side
1973 - 1979 The year of crank manufacture is the last digit in a diamond
1980 - 1984 The year of crank manufacture is the last digit in a circle
1985-Post "11" in a rectangle means 1985, "22" means 1986, and "33" means 1987...

If yours does not have a number inside the diamond or circle you've got a pre-1972.