Ahhh "switches"...it must have been too late. I clearly didn't register this leap.
Yes, well one thought when I did this was that if the bolt went down through the hinge piece it, nothing would fall apart even if the nut were gone. I don't think there will be any appreciable torque on it; it could have been a pin connection with cotter pins.
Tanner, I've seen the axle washers that your describing, and the size might be similar (1-1/4"). I believe that's an option, or Frank's idea of one softer, disposable upper washer.
Another thought occurred to me that I could drill and tap a hole through the top plate, and then bolt down one of those little slotted widgets - like a rim clamp only smaller - up against one flat. I can't think what they are called, but the ones I'm thinking of have an elongated slot for the hole. Some weather-tight box covers use a special washer that is similar. Maybe even a hex standoff (I usually just drill out a coupler nut) located so it mates one flat to the bolt head?
~kitestrings