Like Dan posted most shoulder nut washer combos are for spinner and shaft extenders, but not all.
A couple of years ago I bought some really nice combo sets from Shuttrman.
They have a beautifully machined aluminum washer and a shouldered nut in 1/4-28 with a 12 mm wrench flat.
1/2” would probably work but the 12 mm is a better fit. I prefer to use a combination wrench instead of the four way wrench on props anyway.