[Lucky#13]

I will add only this comment to what kkkriverrats has posted above. I have only seen two trunnions- ever- with a piece mark (drawing number) present. One is on a C&R Remington 1917 that was converted at RIA to a 1919A4. It has several components with the drawing number/RIA mark that I have never seen another example of, or maybe only one other. I know of one other such marked trunnion, that came in someone's kit. Saginaw did put a flaming bomb on some, but apparently not all trunnions. No clue as to why the inconsistency. Never have seen an early steel trunnion, of the Tank or Aircraft gun vintage, with the rectangular bunter plate, so I can't say if Westinghouse, Colt or Marlin-Rockwell marked them or not. I was once told that BA marked their trunnions, but I have never found an example to prove it, so I have my doubts. But as pointed out, there are a variety of markings that are fairly common on trunnions and we have no record of their meaning. That will likely always remain a mystery.

 

[Lucky#13]

Just to add my anecdotal experience, I remember well iRIGHTi's issue, and I believe it was a variation in the thread depth of the trunnions. In working with the new made 1919 Tank Gun/1919A2 Cavalry Gun slotted shrouds, I have also noticed a significant difference in fit between trunnions. Since I know the shop that makes the shrouds is very consistent, I looked to the trunnions and there is no doubt they vary. Every once in a while, one of these buggers just doesn't want to go together easily!