This form of mounting was still being carried during the Japanese campaign in China. Please remember that the dating I gave is an educated guess based upon pictures, which is not the best way to appraise a blade. The modification to the tang of this sword will greatly impact the value of the piece. It is what it is. My first experience with one of these threaded tangs came back in the mid 1970's when I bought a collection of nine swords from a vet. I was very confused when I removed the handle of a shingunto mounting(WW2 era)to find the threaded tang. In all of the swords I have owned over the years, I have only owned three with this nakago modification.