PeterG wrote on Mar 12^th, 2019 at 7:54pm:

FredC wrote on Mar 11th, 2019 at 6:48pm: Peter, In another thread you mentioned the French origin of Krag screws. BR in a very old post alluded to the same. What about the threads do you mean? The number size, the thread pitch or the thread form with the rounded crests and roots?   Based upon my research, the screws are metric, and of French design.  They are 4 mm. and .01 threads.   There is no advantage I can see (other than if one has an all-original, collectable rifle they want to keep that way) to keeping those troublesome threads on one's gun.

Peter, I am going to have to disagree. it looks like the metric dimensions will be closer to 4mm diameter by .84 pitch. The od of the Krag screw is .164 compared to .157 inches for a 4mm screw. Enough different a metric screw would be sloppy in an original barrel. The mismatch in pitch would make it seem tighter that it really is, but it would be more susceptible to stripping.

In this old thread I did all the measurements of a screw pulled form my dad's original rifle:    (You need to Login
An 8-32UNC tap would be a closer but not correct match for retapping an original barrel.
I really like the idea of you rails, even made one for myself years ago. Would have bought one of your instead of making one if they were available then and I had known of them.