My table saw comes with two arbor nuts — one with a flange washer attached for use with a standard blade and the other without a flange washer for dado blade setups. I switch from one blade style to the other pretty often in my projects, and those arbor nuts are easy to knock off the saw. So, I attach the nut I’m not using to the side of my table with a 3/4″ rare-earth magnet. It holds the nut securely and I always know where the spare nut is attached. This would work equally as well for stowing the flange washer of a standard arbor nut.
– Liam Moriarty