Farmall reference

IH Casting Date Code

International Harvester stamped a date into nearly every major casting it poured: the month and day as numbers, separated by marks that look like screw heads, finished with a letter for the year. Learn the letter and you can date any big IH casting at a glance — the second opinion every Farmall serial number deserves.

Letter	Year	Letter	Year	Letter	Year
I	1939	O	1945	U	1951
J	1940	P	1946	V	1952
K	1941	Q	1947	W	1953
L	1942	R	1948	X	1954
M	1943	S	1949	Y	1955
N	1944	T	1950	Z	1956

Worked example

A code reading 1·29·J is January 29, 1940 (J). If that casting is the block of a Farmall H whose serial decodes to early 1940, everything agrees — castings were poured a few weeks to a few months before the tractor was assembled and serialized.

The limits, honestly

The letters repeat in later cycles (the alphabet starts over after Z), so a letter alone brackets a year within a model's production run — it does not stand alone across eras.
Casting dates date parts, not tractors. A newer casting on an older tractor means that part was replaced; dealers and farmers swapped blocks, heads and housings for decades.
Replacement and service castings exist with later codes. One odd code is evidence to weigh, not a verdict — the pattern across several castings is the verdict. How to run the full two-numbers check.

The $39 Buyer's Check Kit

The decoder gives you the year. The kit gives you the rest of the check before money changes hands: serial-verification worksheets, the two-numbers check that catches swapped engines, year-split parts traps, and an inspection checklist for each family.

Included in the $39 Buyer's Check Kit

See what's inside