Father-Son 1974 Duster Project

I am having problems finding the nut that holds the steering wheel on the column shaft. The threaded part of the shaft is larger than 1/2". Tony DeFeo sent me a nut and washer and it is obviously too small. The washer won't even fit on. I don't have calipers but if I snug an adjustable wrench on the threads it's easily a 1/16 bigger than a 1/2 bolt. The nut tony sent me although fine thread will begin to thread on a 1/2 bolt...