I got mine through the local hardware store, I've been runnin it for over 20 years now with no problems. I guess some are more anal then others about stuff?? Good Luck
The washer has a countersink that the "special, split acorn nut" seats into. The nut goes on and looks upside down since the acorn part points towards the washer. They don't make them any more but you can find variants that will work. Similar design, but not exact copies.
