Lets talk about measurements in 1861.



The gun makers in Liege, Belgium, used the metric system. So, the threads on the screws in your musket will probably be metric. If the musket was converted in Liege, it should also have metric threads on the nipple.



If it was converted in the "Germanies," you have another problem. The German speaking world used used Schritt (pace) based measurements until the 1870s, at which time the Germans and Austro-Hungarians converted to metric. An Austro-Hungarian Schritt was 29.5 inches long. The Prussian Schritt was a bit different, and there may have been other differences in the other kingdoms, duchies, free cities etc, of the "Germanies." With the exception of nipples for the Muster 1851 Swiss Feldstutzer, I know of no one who now manufactures Schritt based nipples.



Since the U.S. Army copied the Model 1777 French musket when it began manufacturing standard U.S. Army muskets, threads on parts for Springfield weapons were metric until the advent of the 30-40 Krag, at which time Springfield went to inch measurement.



The British operated on the inch system, so nipples for Enfields were threaded in inches.



My experience with Austro-Hungarian Army weapons: The threads on the screws of Muster 1842 muskets, Muster 1844 Extra Corps carbines, and Muster 1844 and 1849 Kammerbüchsen ("Garibaldi" rifles), are neither inch nor metric, ergo they are in Schritt. I don't have a Schritt gage, and know of no one who now makes one. Most of them were converted from tubelock to percussion in Liege before shipment to America for use in the Civil War. In those instances where I've been able to pull the nipples, they have been metric threaded. However, the diameter of the nipple depended on the individual Liege arms house doing the conversion.



The only way to know for sure for your musket is to pull the nipple intact, measure the threads, and then try to find something that works.



This is one reason why logistics in the Civil War was a nightmare.



Good luck!



Don Dixon