The 444 and 544s were almost completely metric.
In my experience the 122s and 140/164 were almost completely unified
threads (inch sizes) except for electrical gear (starters, generators and
alternators) but in 1974 with the advent of the 8-bolt engines
they started a creeping metrication. I scrapped out a 76 245 during
the summer, my first real experience on them, and found a LOT of 8 mm bolts
with 1/2" hex heads. Previous metric experience with metric stuff showed
that 8mm bolts usually had 12 mm heads, which would be rounded by a 1/2"
wrench. Maybe they had 5/16" bolt blanks and rolled metric threads on them....
The biggest difference is that the metric thread on the 8mm bolt approximates
20 threads/inch. In a pinch back in my 544 days (35 years ago) I used an
adjustable bolt die to put 20 threads on a 5/16" bolt for an 8 mm need.
In case of doubt, better get out the pitch gage!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma