that's a good idea, maybe I'll try it, I'm worried about burrs though, the fit of the hub on the shaft is pretty precise and if the shear pin does its usual thing it will make a little burr on the shaft at the hole and I'm worried about scoring the inside of the hub. With the plastic hub it isn't an issue, the fit is a lot sloppier to begin with. I may do an external retaining collar and slot the hub so it will squeeze onto the shaft. I want to preserve the ability to shear around if the head hits something.

I've always used the stock pins, haven't tried the paper clip. May have to with this one, just put the clip thru the screw holes and the shaft hole, since the clip is softer it might not leave a burr when it shears.