Hi Wolfe. Welcome to the Forum. I'm not sure what you mean by a "single screw". In general revolver prices vary greatly based on rarity and condition, accessories (e.g. original box etc) and in this case probably model number. The 686 has been thru numerous engineering changes starting with the plain 686 (no dash), and progressing thru 686-1, 686-2, etc, to today's current production 686s. Value will vary somewhat between the different changes, with the older models usually being valued slightly higher assuming similar condition. Hope this helps.