Date coding explained

[TwoTees]

the 4 253 i have here are : 12J3, 18J8, 16G2, 31A9. I think i still have one or maybe two in the back of my dads shed.

how does the coding and numbering system work. how do you match one to your cars manuf date??

eg. from above
12J3 = 12th(12), 9th month september(J), 1973 (3) or if its blue it may be 1983

i is not used in the month section I think.
This date needs to be near your build date.
There is a thread on it in the technical section.

EDIT: http://www.mysandman.com.au/forums/showthread.php?t=570
Chris