Smith & Wesson N frame thumb piece nut, blue $10.00 Part 21 on the exploded diagram. Used, excellent condition blue thumb piece nut from a Model 57, N frame revolver. Will fit other models of N frame revolvers. In stock Smith & Wesson N frame thumb piece nut, blue quantity Add to cart Category: Smith & Wesson Related products S&W 39/439/3904 series XP magazine springs 3 pak $34.97 S&W 6904/4006 series XP magazine springs 3 pak $34.97