Drillbit,
Most of the Yale serial numbers are 6 numbers long and set in blocks. From 1958 to 1968 the serial number would have stated with letters. AB = 1960, AC = 1961and so forth. From 1969 to 1994 all serial numbers run in blocks. 1973 runs three different sets. 213739 - 219999, 220000 - 232908, 230000 - 242000. Each year is like this up to 1994. Then they went with a 11 digit alpha numeric serial number. Good Luck
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.