I use 0.040” dia. Stainless steel.
IHO, ... there's no need for expensive wire for the "A". I've had the HF wire on for 5-1/2 years and just recently removed the wire retaining the flywheel bolts when I did my Hillbilly valve job. Surprisingly, it looked exactly as it did 5-years ago when installed, clean and shinny. I marked the bolt heads with a white paint marker and they didn't moved. Now, if this was an aircraft, I'd use the expensive stuff, but we are talking about 4.22:1 compression with 24.5 horses at the tires.Get from aircraft parts suppliers- will be of highest quality.
What is the correct wire gauge for securing bolts that need to wired, e.g. flywheel bolts?
The specification looks like bailing wire to me.Since you are asking what is correct, here is just one print that I have from the archives that shows the part number, the diameter of 0.045" - 0.49", and the length of 11½ - 12" of the flywheel safety wire. Ford's assembly line workers did not just use a coil of wire and reel-off a random length to use on each engine like we do today. Instead, the Ford Engineers assigned a specific part number for all items used including ALL fasteners and safety wire that made-up that component.
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I have not used safety wire on the flywheel or rods in some time and I drive hillclimbs. No problems