The thread direction was changed from right-hand to left-hand when S&W received reports in 1959 the extractor rod on 44 Magnums (only this model as far as I know) was loosening due to recoil and locking up the cylinder, thus preventing the revolver from being opened. The company decided to change the thread direction on all K and N extractor rods and extractor stems and issued Engineering Directive #586 on December 22, 1959. The reason for the change: To prevent extractor rod and extractor stem from loosening. Depending on the model, it took nearly three years to implement.

Bill