No-Drill, Scope/Aimpoint Base Takes Magnum Recoil
Quickly converts popular, adjustable-sight revolvers to accept compact scopes (using Weaver-style rings) or Aimpoint. On Smith & Wessons, a special "nut" is installed into the rear sight recess.
Big Book Catalog, Issue:65, Page:240
SPECS: 5¼" (13.3cm) long. Black- (blued) or clear- (stainless) anodized aluminum base, steel nut. S&W fits K/L/N models originally equipped with adjustable sights and barrels 5½ long or longer. Does not include rings.