I was going through the specialty nut bins at Home Depot when I found these
brass plated Knurled nuts in the proper thread size for Champion Spark plugs there were 3 in the pkg for $1.09 so I said why not
there is one draw back they are larger than stock but if your old Arthur acts up they are easier to unscrew.
Yep, 8-32 for the brass hat plugs. For the earlier plugs with a 5-40 thread you have to get them from RV or make your own.
For the 5-40 thumbnuts I get 4-40 thumbnuts, drill and re-thread them...
: ^ )