Right, I have had a look and see what this is...it first looked like the sear, but they call this the hammerTo be more precise (on mine) it's the two outer edges that make contact/do the work, these have been polished/worn to give a good clean let off. The pressed steel parts on the insides seem to be to add strength/rigidity (they call this the internal hammer). This engages with a pressed steel part (they call the pawl...this seems to be the sear) that in turn is operated by the trigger.