One of the Smith and Wesson books shows the original order by Patton dated Sept 9, 1935, 3.5” barrel, McGiven bead, sighted for 15 yards dead center hold with S&W .357 Magnum ammunition, added the Wesson grip adapter.
Serves the same purpose as the Tyler T-Grip Adapter, i.e., keeps the middle finger from riding up into that otherwise empty space, thus giving greater leverage for double action shooting.