Interesting topic!
I dont think there is a rule of thumb, and I think application of these fixtures sort of depends on period, makers assembly processes etc.
It seems with the 1845 (British) patterns (many M1821 still produced about then) there was a steel washer indeed for tightening hilt assembly....but over that was a leather or other material one which indeed served as a moisture guard.
In medieval times there was a rain guard at the crossguard which covered the mouth of the scabbard to prevent rain and moisture from entering.
I think for purposes of restoration, which I presume is the goal here, it would be necessary to determine this from other examples of the sword being considered. Its sounds as if there was a degree of latitude rather than any rule of thumb for all.
|