The "washer thingy" is called a "prop washer" and the nut is a "prop nut". These must be tightened down quite securely. We both know you don't have a LHS locally and no a home depot part won't work(extremely hard steel). You could probably borrow these for the weekend at the field while waiting for shipment from Tower or somewhere else. Did you have a spinner on? It probably would have captured the now missing hardware. Tighten nut with a 4-way or combination wrench. I use a socket wrench, 1/4 drive, myself. Don't want to break or strip anything but must be tight. Be glad prop didn't fly into your face. parts will only cost a couple of bucks and you can research and find at Tower. Gives you an excuse to order more stuff if you want. you know, glue, planes whatever. Good flying this weekend. I'll be here in morning and hopefully have flying weather by lunch time.

Bruce

What kind/size of engine was it again?