The Ruger Single Six is really several diferent guns: The original Three Screw Single Six, and the New Model Single Six, bot of which were available as "Super Single Sixes" with adjustable sights. And then there was a Vaquero version with color cased frame and the grooved topstrap rear sight. (Fixed sight Single Sixes have a dovetailed rear sight in sort of a flat top frame.)
Three Screw models, without the transfer bar conversion, bring a premium price, preferred by collectors and shooters alike.
Bob Wright