The coup-de-grace, and I fit the lower skin of the flight-deck and tighten the bolts up after riveting as previous. Those are M6 bolts, beloved of the Honda motorbikes I used as a teenager, and they are driven into the ends of the rotor-arms. If you want to go belt-and-braces, glue them in to and pop-rivet all round.
The FAA might be chary of the method in the absence of welding, but believe me you could hang one of your neighbours without these babies giving way.
If you are really anal, however, you can drive a threaded rod in steel (heavy) or nylon (light) all the way through from one end to the other... but my way's the high way.
Note the all important "U/side" moniker in permanent marker, essential if your Huey-style skids are not to be fitted facing the wrong way up.
