There are no plastic hammers for the metal receiver pistols, only steel. First and second generation 9mm pistols had forged steel hammers with half-cock notches. Near the end of the production of the second generation pistols, S&W deleted the half-cock notch. Late production third generation pistols introduced MIM triggers, sears, and hammers.
You can install a forged steel hammer with the half-cock notch, but I do not see the half-cock notch as having a real function with the second or third gen pistols as the second and third gen pistols have a firing pin safety. The half-cock notch will make the double action pull seem to have a hitch as the sear drops into the notch.
