from Google, changes to 586 & 686 over the years:
Model 586 Variants[edit]
586, 1981 Intro
586-1, 1986 Radius stud package, floating hand.
586-2, 1987 Change hammer nose and associated parts.
586-M, 1987 Product warning by S&W, M overstamp to indicate factory (mod for 586 and 586-1)
586-3, 1988 New yoke retention system. 1992 Delete 8 3/8" barrel and four-position front site. 1992 Delete nickel finish
586-4 1994 Drill and tap, synthetic grips, change rear site and extractor. 1995 Delete square butt. 1997 Delete 8 3/8" barrel, change to MIM thumb piece.
586-5, 1998 Change design to eliminate cylider stop stud. Change to MIM hammer with floating firing pin, change to MIM trigger, change internal lockworks.
586-7, 2006 Limited Edition. 7-shot variant only.
586-8, 2012 Reintroduced under Smith & Wesson's Classic lineup. 6-shot only.
Model 686 Variants[edit]
The Smith & Wesson Model 686 is a stainless-steel version of the post-1980 L-frame revolver.
686 no dash, introduced model
686-1, 1986, radius stud package, floating hand
686-2, 1987, changed hammer nose, bushing and associated parts
686-3, 1988, new yoke retention system
686-4, 1993, change rear sight leaf, drill and tap frame, change extractor, hogue grips
686-5, 1997, change frame design to eliminate cylinder stop stud, eliminate serrated tangs, change to MIM hammer with floating firing pin, change to MIM trigger, change internal lockwork
686-6, 2001, internal lock