Firstly, my thanks to LynnC, Clark, and especially Ken for putting me on to the fact that these might be metric threads on the jaw screw.
Spent a few hours today checking and measuring, and playing detective.
This is what I've come up with.
The thread in the cock to accept the jaw screw is definitely a M8 - 1.25
Checked this many times to confirm this.
As shown in a previous post, the thread on the jaw screw is a M7-1.5.
So, it appears, that sometime in the past 211 years, probably closer to less than 50 years ago, the original jaw and jaw screw were lost and an attempt was made to replace it, either for aesthetic reasons, or to try and make it workable.
Whomever put the 7mm screw in a 8mm hole attempted to close up the hole with a series of blows on a centering punch around the circumference of the hole to peen over the top of the hole.,
The marks can be seen on the above photo.
It appears that the jaw and jaw screw were definitely matched as the hole in the jaw is 7mm.
It was not possible to run a 8x 1.25 bolt into the hole because of the peening, so I carefully ran the proper tap in to clean up and relieve the top of the hole.
Have to finish the process now with a bottoming tap now on order, but the thread looks good, and the only part showing any cutting is the peened area.
I was able to get a M8 x 1.25 bolt partially into the hole. Bottoming tap will resolve this.
The cock appears hardened, so I'm glad there's not too much cutting involved.
Now the decision has to be made as to how to treat the new jaw screw.
My choice right now would be to tig weld on a new 8mm bolt with an unthreaded portion very close to the flange of the existing jaw screw that I have.
That would mean cutting off most of the 7 mm thread that is there now.
Then file the welded area down rather than size it in my lathe. Then I would file open the hole in the jaw to accept the 8mm shaft.
Since there is not a rush to repair this, I will in the meantime see if I can find and purchase a proper and original jaw and jaw screw.
Would appreciate any comments and suggestions.
Right now, I don't feel this repair as I just outlined would deter from the value or patina of the flintlock.
I'm kind of an antique myself with replacement knees, and I feel I'm just as desirable as I was before the knee replacements!!