The first Item #46 is a hammer for a blue gun (BL) with the spur width of .265 inches. The middle item #46 is the same width hammer for a stainless steel gun. (SS). The third Item #46 is for a stainless steel gun with the "semi-target" spur that is .375 inches wide. The standard hammers are the .265 version. These usually came standard on fixed sight revolvers like the Model 64. The Semi Target hammer was an option for the fixed sight revolvers and was usually standard on the adjustable sight models (Models 14, 15, 19, 67, 66 etc). You could upgrade the adjustable sight guns to a full target hammer which has a spur that is .500 inches wide.

Hope this helps.

Steve