Boxcarman;
Morning sir, I trust wherever this finds you, it finds you well other than the ring screw dilemma.
Funny that we just went through the very same dance in my shop two days ago with some mystery rings that buddy had.
In my stock of strange and odd screws, I have 6-40, 6-48, screws labeled "Weaver Ring Screws", screws labeled "Redfield Ring Screws" and then the "Misc. Metric" screws....
Wouldn't you know it, none of them was exactly correct.
We figured it out this time, next time I believe we'll tap the hole in the ring to a screw I actually have.
It's almost like the ring manufacturers made their own thread pitch sometimes.
Reminds me of a woodworking machine I was repairing that ended up with Whitworth threads and it was only that the machine shop I took it to had an Irish machinist who recognized them.
A tip of the hat to the gentleman offering some of his stash too by the way.
All the best.
Dwayne