Old GMC Gold,
The way I deciphered the chart was that yes C is for Commercial.
The 1st # is The Thread size.
The 2nd # is the heat range.
And the suffix is different apps.
I E C44N to me now translates to a Commercial grade 14mm threaded plug,
With a heat range of 4.
The N makes it a 3/4 inch reach into the chamber and the Threads are 3/8 of an inch Long.
I know it will fit the head BUT will it stick into the combustion chamber Too Far?
Thanks,
steve sr.
