Right, I have had a look and see what this is...it first looked like the sear, but they call this the hammer To 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.