This makes up at least half of the gun's mass right here. This is the assembled hammer mechanism outside of the case. The output shaft is held all the way down to the rest of the mechanism by the front bushing. The large dark chunk at the bottom is the flywheel, the lighter piece settled inside of it is the clutch, and the shaft on top is obviously the output. The motor will rev up the flywheel, and a cam buried down in the center will kick the clutch up towards the shaft as the flywheel overtakes the output shaft. The clutch piece will be caught between the flywheel grooves and the three tangs of the output shaft, and you get an impact. Nobody I've shown this to so far have seen this exact kind of impact mechanism except on a hydraulic gun. When I took it apart the grease in here was almost like tar in some places. I don't know it it was just old or if it's a special-purpose grease. It's going back together packed with wheel bearing grease.